A STUDY OF POA PRATENSIS, L.
BY W. J. BEAL.
IN noticing the variations of Poa pratensis in my recent studies, I am
constantly confronted by this question : Are the variations due
entirely to the surroundings as we find them at Agricultural College,
Michigan, or to some extent to the seeds from which the plants were
raised?

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The plants examined were selected in various places in one neighborhood, but as to the source of the seed, I know nothing. If I knew
the plants were from seeds of one selected plant, even then I should
by no means feel sure that any variation in the products were entirely
due to the surroundings and treatment of the soil. With these preliminaries, I will briefly state the results of some studies.

I examined a large number of specimens when in flower or later.
From these I selected ten culms in variety, including the longest and
the shortest. The mode of comparison is here illustrated by lines.

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Ten horizontal parallel lines, each represents the average of the ten specimens. There are five vertical lines. I do not here illustrate or speak
of the stamens, pistils, palea, glumes, or grain. I speak of the
lengths of the internodes, leaf-sheaths, blades, panicles, width of panicles, length of the longest branch, the total number of spikelets of
each plant.

The tallest plant grew on good soil near hoed ground, had
seven internodes, and was 127 c.m., or about four feet high, and contained 570 spikelets; the smallest had five internodes, was six c.m. or
about two inches high, and contained eleven spikelets.

The mode here used to represent the comparison of the plants, I
first saw used by A. R. Wallace, the famous English naturalist. Be-
ginning at the left in Fig. I, I added the figures representing the
length of the ten top internodes and took an average. If number one

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was above the average, as it was, the part and the proportion is shown
by putting it above the average; if below the average, the line goes
below. In like manner I compare the ten next internodes on the
second perpendicular line, and the next below on the third vertical
line, and so on.

Let us follow the lines representing the tallest plant clear
through. Begin with Fig. I, on the top dotted line. We see that it
runs in a zigzag manner where the internodes are represented, different lines for the sheathes, and still different for the blades, and still
different for the panicles. In other words these several parts differ
from the medium or average in different degrees. Then trace the second, the third, and any or all of the others. We find of the first or
upper internodes, six above the average and four below; of the second internodes, five above and five below; of the third internodes,

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four above and six below ; of the fourth internodes, three above and
seven below ; the fifth is too short to show well.

Of the first sheath in Fig. 2, there are six above and four below;
of the second sheath the same; of the third sheath four above and

four below, and two are not shown. In case of the first blade of a
leaf, there are five above and five below ; of the second, four above and
six below. Of the total length of panicle, there are six above and four
below the average. The total width and the proportion of the longest
branches are represented by finding six above the average and four
below.

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Adding the number of spikelets found on the ten plants, we find
four above the average and six below. This comparison could probably be carried to other parts of the plant. We could select culms
from one plant for comparison with each other, or culms from different plants. We could compare those grown in one locality with those
grown in another. By following up this plan, we could learn which
parts varied most, which least, and thus learn those characters of most
and of least value in defining genera and species.