BRIEFER ARTICLES.

A Study of Silphium perfoliatum and Dipsacus laciniatus in regard
to insects.1
-The upper surface of the leaf of Silphium perfoliatum near
the axis is thickly set with small hairs. Their length is on the average
about 0.17 mm. They are composed of four cells each having a distinct
nucleus; the upper one is somewhat enlarged. Some of the hairs are
colorless, while in some a peculiar brown substance was seen which was
variously distributed, sometimes in masses at the top of the upper cell or
diffused through the upper cell, and sometimes through the lower ones
as well. These hairs point toward the tip of the leaf. Similar hairs were
found all along the mid vein, side veins and veinlets of the upper surface of the leaf, and also on similar portions of the under surface. No
difference was seen between these hairs and those near the axis, except
that they were much more thickly set along a surface about an inch in
length at the base of the leaf. The leaf examined was about 20 cm.
long and was typical.
The brown material does not seem peculiar to the hairs. Upon the
upper surface of the leaves were found some more very small prickles
composed of two cells, the upper very pointed, the lower one globular
and containing an onion-shaped mass of brown matter similar in appearance to that in the hairs. In the epidermal cells of the stalk were found
similar masses, and some cells were completely filled with it.
The cavities formed by the perfoliate leaves are very small and hold
but a few cubic centimeters of water. They are full after any rain or
heavy dew, but are often dry before noon. If cups are dry at night they
will be filled in the morning when there is a heavy dew; otherwise they
will be dry.
These cups do not appear to serve any purpose as insect catchers.
No insects were seen in any of the cups. This plant is not native here,2 
and perhaps it does not show its full development with us.
Is Dipsacus laciniatus insectivorous? To answer this question was
the purpose of the following observations:
It is well known the connate leaves of this plant form cups sur-

1 Read at meeting of A. A. A. S., New York, August, 1887.
2 Lansing, Michigan.

rounding the stalks, which most of the time contain more or less water.
It has been suggested that the purpose of this arrangement is to catch
insects for the nutrition of the plant.
A microscopical examination of the leaf surface was made, to discover,
if possible, any peculiar organs of absorption. Especially was that portion of the leaf explored that is much of the time beneath the water in
the cups. On this portion of the leaf were found two forms of hairs.
The more numerous were about .09 mm. long, with a club shaped upper
portion upon a pedicel composed of a single cell. The upper part was
composed of about five nucleated cells; it was broader than thick, and
seemed to be divided by a partition across the narrow way. These hairs
were all inclined toward the tip of the leaf with the broad side toward
the leaf surface, and were not very numerous. The rarer form of hairs
had a rounded head upon a pedicel of a single cell. The head was divided
into a number of cells which contained no visible nuclei, but were generally filled with brownish-green masses of granular matter.
Other portions of the leaf were also examined, and upon the whole
upper surface along the mid vein, side veins and veinlets, were found
hairs similar in form to these and equally numerous. They were also
found on the corresponding portions of the under surface of the leaf.
So far as special organs of absorption are concerned, that part of the leaf
below the surface of the water shows no advantage over any other part.
Twenty plants were watched carefully for two weeks, and during
that time but few insects were caught, and those were mainly bees; the
nutrition from the insects caught could be but little.
Water was gathered from several plants ten days after a rain, when
it had evaporated largely and must have been concentrated. The water
was filtered from suspended matter, mainly algae and flower petals, and
the starch-iodine test applied, first for nitrites and then for nitrates, and
no indication was obtained of the presence of either. If present at all,
they were in extremely small amounts. Nessler's test for ammonia gave
a marked reaction, showing the presence of from one to two parts of
ammonia in 1,000,000. To take advantage of so small an amount of
ammonia hardly seems sufficient cause for such a modification of the
leaves, with no special organs for absorption. It would seem that the
plant might get some good from the ammonia in the water, and perhaps
these hairs may absorb the nitrogen compounds from air or water. But
this supposition would include all similar hairs on both surfaces of the
leaves, and would not account for the cups; it can only be an incidental
advantage, therefore, and not the prime use of the water-gathering cups.
Dipsacus depends mainly on the rain for its water supply, and very
little upon the dew. Some cups were thoroughly emptied, and it was
found that after a heavy dew there would be a little water in the cups.
This would tend to replace that lost by evaporation, but this loss is slight

because the water is so well shaded from the sun. Upon July 20, there
was a copious rain that filled all the cups, and it was five days before any
marked diminution of the water was noticed. At the end of fourteen
days many of the lower cups still contained water. The cups were found
to contain from 300 to 600 cc. An average plant would hold about a
liter, and a large plant as much as a liter and a half.
It seems more probable that the object of the cups with their water
is to protect the plant from crawling insects, which it does most effectually. The blossoms are frequented by bees and other flying insects, but
upon the plants are found no ants or other crawling animals. The
hooked prickles so thickly set along the stems, and especially on the
stem just beneath the blossoms, are a perfect barrier against snails, slugs
and such soft-bodied animals, while the water keeps away the hard-bodied insects. The flowers are not well arranged for cross-fertilization
by ants, as the anthers and stigmas are raised so far above the throat of
the corolla that ants would not reach them easily and naturally.
It is doubtless to the advantage of the plant that such insects be kept
away, as they would take the nectar and yield nothing in return.
It is perhaps worthy of notice that no bridge is thrown across this
moat until the falling flowers cover the surface, and then it is too late
for them to be injured by marauding ants .- W. J. BEAL and C. E. St. JOHN.