After an interval of 30 m. the apex was observed, and
it was seen to cross a little obliquely two divisions of the micrometer in
9 m. 15 s.; and after a few minutes it crossed the same space in 8 m. 50s.
The seedling was again observed after an interval of three-quarters of an
hour, and now the apex crossed rather obliquely two divisions in 10 m. We
may therefore conclude that it was travelling at about the rate of 1/50th
of an inch in 45 minutes. We may also conclude from these and the previous
observations, that the seedlings of Phalaris in breaking through the
surface of the soil circumnutate as much as the surrounding pressure will
permit. This fact accounts (as in the case before given of the asparagus)
for a circular, narrow, open space or crack being distinctly visible round
several seedlings which had risen through very fine argillaceous sand, kept
uniformly damp.
Fig. 51. Zea mays: circumnutation of cotyledon, traced on horizontal glass,
from 8.30 A.M. Feb. 4th to 8 A.M. 6th. Movement of bead magnified on an
average about 25 times.
Zea mays (Gramineae).
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