50) shows that the apex moved to one side, but changed its course ten
times in the course of the ten hours of observation; so that there can be
no doubt about its circumnutation. The cause of the general movement in one
direction could hardly be attributed to the entrance of lateral light, as
this was carefully guarded against; and we suppose it was in some manner
connected with the removal of the earth round the little seedling.
Fig. 50. Phalaris Canariensis: circumnutation of a very young cotyledon,
with a mark placed below the apex, traced on a horizontal glass, from 11.37
A.M. to 9.30 P.M. Dec. 13th. Movement of apex greatly magnified, here
reduced to one-fourth of original scale.
Lastly, the soil in the same pot was searched with the aid of a lens, and
the white knife-like apex of a seedling was found on an exact level with
that of the surrounding surface. The soil was removed all round the apex to
the depth of a quarter of an inch, the seed itself remaining covered. The
pot, protected from lateral light, was placed under the micro-
[page 64]
scope with a micrometer eye-piece, so arranged that each division equalled
1/500th of an inch.
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