A CCMPARISON OF VIGOR 95mm: saws AND CROSSES OF THE FLORIST
GLcocINIMSINNINGIA SPHSIOSA BENTH. AND HOOK.)

By
JAMES GLYNN KARAS

AN’ABSTRACT

Submitted to the College of Agriculture of Michigan.$tate
University of Agriculture and.Applied Sciences
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1958

 

 

 

JAMES GLYNN KARAS ABSTRACT

This study is an attempt to compare selfs and crosses in the
florist gloxinia (Sinningia speciosa Benth. and Hook.) for which
there is neither a report nor systematic commerc1al utilization of
heterotic behavior.

All possible combinations of fifteen parental plants were
attempted. Seed from the eight plants judged highest in fertility,
as evidenced by available seed, was used in the present study.

Dry weight as a criterion of vigor did not permit the
successive determinations of vigor on the same plant that were
needed to construct the characteristic growth curve. Maximum
diameter, which correlated + 0.867 with dry weight, permitted
successive determinations.

The expressions of heterosis noted, specific combining
ability, and vigor contributed by individual parental plants
are summarized graphically and tabularly. The extent of
heterosis noted compared favorably with that reported in corn,

onions, Sorghum, and snapdragons.

A COMPARISON OF VIGOR BETMBEN SBLFS AND CROSSES OF THE FLORIST

GLOXINIMSIMJMIA SPEIZIOSA BENI‘H. AND HOOK.)

BY

JAMES GLYNN KARAS

A THESIS

Submitted to the College of Agriculture of Michigan.State
University of Agriculture and Applied Sciences

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1958

ACKNOWLEIIEIJIENTS

The author wishes to express his gratitude to Professors
U. D. Baten and H. M. Brown for their assistance.

Sincere appreciation is extended to Dr. W. J. Haney for
suggesting the problem and for constructive advice.

The writer is indebted to Professor P. R. Krone for
arrangement of financial assistance during the term of
this project.

The writer would like to express his gratitude to
Professor J. R. Culbert of the University of Illinois,
whose assistance and confidence has inSpired the author

in this work.

TABLE OF CONTENTS

Page
INTRODUCTION...................... 1
REVIBUOFLITERATURE.................. 2
PRCISEDURE .......................

REULTSOOOOOOOOOOOOOCOOOOOOOOOC

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DISCUSSION . O O O O O O O O O O O O O O O O O O O O . .
COMLUS IODS o o o o o o o o o o o o o o o o o o o o o o 13
BIBLImRAH-{Y O O O O O O O O O O O O O O O O O O O O O O 11‘

APPEDDROOOOOOOOO.OOOOOOOOOOOOOO 16

INTRODUCTION

This study is an attempt to compare selfs and crosses in the
florist gloxinia (Sinningia speciosa Benth. and Hook.) for which
there is neither a report of nor systematic commercial utilization
of hybrid.vigor.

Heterosis is indicated when.the expression of a given character
in the F1 is above the mean value of that character in the parental
selfs. Heterosis is specifically, a similar degree of expression in
less time or greater expression in the same time.

Shull (19h8) points out that he originally proposed the term
"heterosis" as a means of providing a concise term free from any
implication of the mechanism involved. Prior to the introduction
of this term, the literature was pervaded with such cumbersome ex-

pressions as "heterozygosis" and "stimulus of heterozygosity".

REVIEW OF LITERATURE

The precise mechanism responsible for the extreme manifestations
of vigor and other characteristics which biological scientists collec-
tively call heterosis has long been a puzzling situation. Numerous
accounts in the literature postulate the apparent mechanism.

Ashby (1930, '32, '37, '39) suggests that certain hybrids manifest
heterosis as a result of a larger embryo (greater initial capital). He
attributes reciprocal differences to differences in embryo weight.
Ashby (1939) found a high correlation between seed weight and dry
weight at floral initiation in the tomato. Transplanting destroyed
this correlation. Furthermore, the growth curve of the hybrid was
essentially parallel to that of one parent (1930).

Passmore (l93h) with reciprocal crosses of Cucurbita'pgpg shows
that plants from larger embryos are larger during earLy growth; whereas,
plants from small embryos attain the same size, but require a longer
season.

Luckwill (1939) in tomatoes suggests that greater hybrid seed
weight is not always indicative of heterosis. Whaley (1939a) states
that existence of heterosis in a hybrid is not necessarily the re-
sult of a larger embryo.

Cowan (l9h3) relates that previous work shows that hybrid
vigor is greatestin.single crosses between lines possessing the
greatest genetic disparity.

Brieger (1950), in work with maize, states that heterosis does

not affect the organism as an entity, but merely individual characteristics.

Luckwill (1939) POints out that heterotic behavior can express it-
self differentially in respect to various traits, portions of the life
cycle, and parts of the organism affected.

Burdick (195h) shows that some hybrids express the maturity genes
of one parent at one stage and those of the other at another stage of
development.

Whaley (1939b) found in gycopersicum.that nuclei decrease to a
smaller size in the hybrid than in the inbreds. Furthermore, cell
and nuclear size in the meristem decrease more slowLy in the hybrid
than in_the inbreds. Fundamental metabolic differences could be
responsible.

Luckwill (1939) found that early flowering is almost completely
dominant to late flowering in crosses of cultivated varieties of
_gycopersicum esculentum, while in intraspecific crosses, earLy
flowering was dominant only when a primary growth factor such as
dwarfness or brachytic stem was involved. Interspecific crosses
produced intermediate flowering hybrids.

Burdick (19510 found that early fruiting is a manifestation of
heterosis in the tomato; however, it is not apparent until the first
ripe fruit. Haskell and Brown (1955) found that varietal hybrids of
tomatoes express heterosis mainiy as earLy fruit yield and more stable
yield than commercial'varieties under varying environmental conditions.

Tables one and two show diversified reports of heterotic behavior

in agriculturally important plants. Basic variations in heterotic

criteria, as well as morphological and genetic variations, do not
allow comparisons between the plants listed. However, this does
give an indication as to the extent of heterosis reported in the

crops.

PROCEDURE

All possible combinations of fifteen parental plants were
attempted with varying degrees of success. The populations used
in the present study were produced from seed matured by the eight
plants judged highest in fertility as evidenced by available seed.
Parental plant descriptions are given in table three. Twenty-
five of the twenty-eight possible combinations were obtained.

Approximately 11.2 cubic millimeters of seed was sown on
steam pasteurized Sphagnum moss over a mixture of equal parts of
shredded peat moss, soil, and silica sand in three-inch pots. The
pots were placed in pans and covered with plastic to provide uniform
germination conditions. .A complete, high analysis fertilizer in
dilute solution provided adequate and uniform fertilization during
subsequent growth.

Seven weeks after sowing, the vigor of the seedlings in pots
was determined visually with a graded series of five standards. The
standards encompassed the entire range of vigor in.the pepulations
and differed by approximately equal growth increments.

As soon as the plants were of sufficient size, they were
transplanted two inches apart in flats filled with a mixture of
three parts peat moss, one part Conover silt loam, and one part
sand.

For correlation of maximum rosette diameter and dry weight, data
were obtained from three ISO-plant samples containing twenty-five

plants from each of three crosses and three selfs. Samples were

evaluated at two, nine, and fourteen weeks after transplanting. At
these intervals, diameter measurements were made of all remaining

plants.

RESUETS

Figure one shows percentage distribution of vigor classes of
cross and self populations seven weeks after sowing. The largest
selfs are equal in vigor to the largest crosses at this time. Vis-
ual comparisons were made with a graded series of five standards,
since measurement of vigor by dry weight or diameter is not prac-
tical at this stage because of the small size of individual seed-
lings. The distribution of the crosses is skewed to the right,
while that of the selfs is to the left.

Figure two shows heterotic behavior of a cross and the two
parental selfs on a dry weight basis. This figure suggests an
increasing growth rate through successive vigor determinations.
A greater mean weight is indicated for the cross than for either
self at all three vigor determinations. This difference increases
as growth progresses.

The most valid basis for determining vigor is dry weight;
however, this criterion does not permit the successive deter-
minations of vigor on the same plant that are needed to construct
the characteristic growth curve. Diameter measurements permit
such determinations. The correlation.of maximum.diameter and
dry weight is + 0.867 for hh9 individual plants representing
three self and three F1 populations.

Figure three shows successive diameter measurements for a

total of five hundred plants of the cross and both selfs. Here

again the vigor differential increases as growth progresses.

Figure four illustrates reciprocal differences. The reciprocals
have a greater mean diameter at all stages than the selfs and show a
smaller vigor differential between reciprocals at the last vigor
determination.than at the second.

Table four is a summary of the means of three consecutive vigor
determinations. The data indicates that parental plants contribute
varying degrees of vigor to their F1 progeny. This figure further
shows vigor means of plants as male and female parents and illustrates
general combining ability. At the last vigor determination thirty-
one of thirty-five crosses were more vigorous than either parent.

Figure five shows frequency distribution of final diameter
means of all populations in units of least significant difference
from the mean of unweighted population means. Evaluation of table
four and figure five indicates that reciprocals of two crosses fall
within the same least significant difference from the mean of means,
two are adjacent, and six are non-adjacent.

Table five identifies parental sources of extreme vigor.

Vigor is shown as the ratio of the second and third diameter measure-
ments to the first diameter measurement. The most vigorous progenies
are distinguished by vigor exceeding twice the grand mean of the ratios
less that of the selfs. Such progeny ratios exceeding 5.7h are ident-

fied by an asterisk.

DISCUSSION

The comparatively greater vigor of the crosses at seven weeks is
shown in figure one.

Ashby (1930) has shown in corn that the growth curve of the cross
and one parent are essentially parallel. However, figures two to four
indicate a materially different growth rate for gloxinia crosses in
which the growth curves are not parallel. This superior growth rate
cumulatively results in a striking increase in vigor, especialLy in
later growth.

Figures two to four illustrate the superior growth rates of the
crosses compared with the selfs. The cumulative increase in vigor
displayed by crosses 3 x l, S x 8, and 8 x 5 for three successive
measurements probabLy is a direct function of the superior growth
rate and initial vigor differences.

Ashby (1939) indicated that the high degree of correlation
between seed weight and dry weight at floral initiation in tomato
is destroyed by transplanting. Data presented in figures two to
four and table four indicate marked heterotic advantage in trans-
planted gloxinia plants.

In figure four the reciprocals show a smaller vigor differential
at the last vigor determination than at the second. This tendency of
the growth curves of reciprocals to converge suggests differential
response to environment. In view of this trend, convergence of the

curves of the reciprocals in later growth would not be improbable,

10

especially in view of Passmore's work with squash (193h).

If the growth curve of the more vigorous reciprocal were to
level off for a sufficient period of time before maturity, it is
likely that a sustained, but initially lower growth rate would be
equivalent to an initially greater growth rate of shorter duration.

The indicated differences in vigor of certain reciprocals shown
in figure four and table four may show maternal inheritance of specific
growth factors in some reciprocals, differentially expressed efficiency
indices relative to specific growth stages in others, an initialLy
larger embryo, or greater seed weight.

.An analysis of final vigor determinations shown in table
four indicates variations in specific combining ability of parental
plants. Those crosses whose maximum diameter at the third vigor
determination exceeds 61.9 (the mean of means, M, by at least twice
the least significant difference) were judged as showing exceptionally
high specific combining ability. The individual crosses l x h, 2 x b,
2 x 7, 3 x 1, 5 x 7, and o x 8 and both reciprocals of 3 x 6, S x 8,
and 7 x 8 exceed this degree of vigor.

Means of specific plants as male and female parents shown in
the margins of table four indicate variation in general combining
ability. Although certain plants are not of high general combining
ability; they, nevertheless, may show high specific combining ability.

The failure of the largest selfs in figure one to maintain the
same relative position in figure five points up Luckwill's (1939)
view that heterosis can be differentially manifested with respect to

portions of the life cycle affected.

11

The grouping of values greater than 5.7h diameters in the lower
right sector of table five suggests apparent heritability of maximal
growth rate in terms of initial diameter for the period indicated.
Evaluating succeeding vigor determinations in terms of the initial
determination serves to eliminate initial size differences between
papulations and to a marked degree permits more realistic progeny
evaluation. The greater ratios of many crosses further shows their
superiority.

Since very complex physiological processes must be involved,
definite conclusions regarding the mechanisms responsible would be
mere conjecture. Furthermore, in view of the almost random selection
of parental plants, the extent of vigor expressed in table four is by
no means the ultimate.

The data presented indicates substantial hybrid vigor in progeny
of certain crosses of the florist gloxinia. Further specific selection
of parental types should produce superior hybrids.

The relatively low degree of vigor present in selfed progeny of
several parental plants in this study would indicate that previous
breeding efforts have been within relatively small distinct pop-
ulations. This is further pointed up by the relative uniformity for
characteristic plant type and pattern in selfed progeny. The marked
degree of vigor noted in certain gloxinia crosses is more often found
in crosses of diverse parentage than those of related parentage as
shown by Cowan (19h3). Additional supporting evidence is indicated

by the relatively high percentage of crosses that were more vigorous

than either parent. Such results would not be expected unless previous

breeding was within relatively small distinct populations.

12

13

CONCLUSIONS

In.this study of vigor of selfs and crosses of the florist
gloxinia, a correlation of + 0.867 for plant diameter and dry
weight validates plant diameter as a criterion of heterosis.

Transplanting is not necessariry detrimental to the ex-
pression of heterosis.

Thirty-one of thirty-five crosses were more vigorous than
either parental self.

Variability among parents with respect to general and
specific combining ability is indicated.

Increased growth rate of a cross in terms of initial
vigor appears to be the result of specific parental plants
and specific combinations thereof.

The extent of heterosis in certain crosses of the florist
gloxinia compares favorably with that reported in corn, onions,
Sorghum, and snapdragons.

The data presented suggest that previous breeding efforts
with the florist gloxinia have been within relatively small

distinct populations.

1h

BIBLIOGRAPHY

Ashhy, E. (1930) Studies in the Inheritance of Physiological Characters.
I. A Physiological Investigation of the Nature of Hybrid Vigor in
Maize. Ann. Bot. hh: h59-h68.

Ashby, E. (1932) Studies in the Inheritance of Physiological Characters.
II. Further Experiments Upon the Basis of Hybrid Vigor and Upon the
Inheritance of Efficienqy Index and Respiration in.Maize. Ann. Bot.
to: 1007-1032.

Ashhy, E. (1937) The Physiology of Heterosis. Amer. Nat. 71: 515-520.

 

Ashby, E. (1939) Correlations between Seed Weight and.Adult Weight in
Tomatoes. Nature lhh: 712.

Brieger, F. G. (1950) The Genetic Basis of Heterosis in.Maize. Genetics

35: AZO-AAS.

British Color Council. (1938 and l9hl) Hort. Color Chart. 2 vol. Banbury.

 

Burdick, A. B. (195h) Genetics of Heterosis for Earliness in the'Tomato.
Genetics 39: h88-505.

Capinpin, J. M. and Alivar, M. A. (l9h9) Heterosis in the Eggplant.
Phil. Agric. 33: 120-lhl.

Coffman, F. A. (1933) Heterosis: Specific not General in Nature.
Science 77: llh-115.

Cowan, J. R. (l9h3) The Value of Double Cross Hybrids Involving Inbreds
of Similar and Diverse Genetic Origin. Sci. Agric. 23: 287-296.

Gartner, J. B., H. J. Haney, and C. L. Hammer (1953) The Effect of
Indoleacetic Acid and Amount of Solar Radiation on Heterosis in the
Snapdragon (Antirhinum majus'L). Science 117: 593-595.

Haskell, G. and A. G. Brown (1955) Hybrid Vigor in Cultivated Tomatoes.
Euphytica h: lh7-162.

Jones, H. A. and G. N. Davis (l9hh) Inbreeding and Heterosis and Their
Relationship to the Development of New Varieties of Onions. U.S.
Dept. Agric. Tech. Bull. 87h pp. 28.

Jones, J. E. and H. D. Loden (1951) Heterosis and Combining Ability in
Upland Cotton. Jour. Amer. Soc. Agron. h3: Slh-Slo.

15

Karper, R. E. and J. R. Quinby (1937) Hybrid Vigor in.Sorghum.
Jour. Heredit 28: 82-91. A

 

Luckwill, L. C. (1939) Observations on Heterosis in gyCOpersicum.
Jour. Genetics 37: h2l-hh0.

Odland, M. L. and C. J. N611 (l9h8) Hybrid Vigor and Combining
Ability in Eggplants. Proc. Amer. Soc. Hort. Sci. 51: hl7-
h22.

Passmore, S. F. (193h) Hybrid Vigor in Reciprocal Crosses in Cucurbiha
pepo. Ann. of Bot. h8: 1029-1030.

Robinson, H. F., R. E. Comstock, A. Khalil, and P. H. Harvey (1956)
Dominance vs. Overdomlnance: Evidence from.Crosses between
Open Polllnated.Varieties of Maize. Amer. Nat. 90: 127-31.

Shull, G. H. (l9h8) What is HeterOSls? Genetics 33: h39-hh6.

Stewart, D., J. 0. Gaskill, and G. H. Coons (19h6) HeterOSls in
Sugar Beet Single Crosses. Proc. Amer. Soc. Sug. Beet Tech. for
19h6.

Thompson, A. E. (1956) The Extent of Hybrid.Vigor in Spinacn. Proc.
Amer. Soc. Hort. Sci. 67: th-hhh.

Unrau, J. (19h?) Heterosis in Relation to Sunflower Breeding. Sci.

Agric. 27: h1h-h27.

Whaley, W. G. (1939) Developmental Analysis of Heterosis in gycopersicum.
I. The Relation of Growth Rate to Heterosis. Amer. Jour. Bot.
26: 609-6100

Whaley, W. G. (1939) .The Deve10pmental Anaylsis of Heterosis in
Lycopersicum. II. The Role of the Apical Meristem. Amer.
Jour. Bot. 26: 682-690.

 

APPENDIX

16

I.

II.

III.

V.

I.

II.

III.

V.

17

LIST OF'TABLES

Some of the Reported Expressions of Heterotlc Behavior.

Other Reported Manifestations of Heterosis Permitting More
Complete Comparisons than those in table one.

Description of Parental Plants.

Vigor Determinations Expressed as Maximum Diameter in MM. at
Two, Nine, and Fourteen Weeks (Upper, Middle, and Lower Figures
Respectively).

Ratios of Nine (Upper) and Fourteen (Lower) Week Diameters in
Terms of Initial (Two Week) Diameter. _

LIST OF FIGURES

Frequency of Vigor Classes of Crosses and Selfs at Seven Weeks
EXpressed in Per Cent.

Dry Weight in.Mg. of Selfs and F of Two Parental Plants (Each
Point Represents Mean.of Twenty-five Plants).

Mean Maximum Diameter in MM. of Selfs and Fl's. The Same Plants
Used at Each Vigor Determination.

Comparative Vigor by Maximum Diameter in.MM. of Selfed and
Reciprocal Progenies.

Frequency Distribution of Mean Vigor for all Selfs and Crosses
Fourteen Weeks after Transplanting, in Units of Least Significant
Difference (LSD ' b.77) from.the Unweighted.Mean of Means (M).

18

 

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FIGURE ONE
FREQUENCY OF VIGOR CLASSES OF CROSSES AND SELFS

AT SEVEN NEBiS IKPRESSED IN PER CENT

35 Crosses(X)
8 Selfs(0)

 

Vigor Classes

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