These small cells were arranged in
longitudinal rows, and varied from 4 to 7 in number; and the cells
themselves varied in length in different parts of the
[page 120]
same pulvinus and in different individuals. In the accompanying figures, A
and B (Fig. 64), we have views of the epidermis* in the middle part of the
petioles of two seedlings, in which the pulvinus was for this species well
developed. They offer a striking contrast with the pulvinus of O. rosea
(see former Fig. 63), or of O. Valdiviana. With the seedlings, falsely
called O. tropaeoloides, the cotyledons of which rise very little at night,
the small cells were still fewer in number and in parts formed a single
transverse row, and in other parts short longitudinal rows of only two or
three. Nevertheless they sufficed to attract the eye, when the whole
petiole was viewed as a transparent object beneath the microscope. In these
seedlings there could hardly be a doubt that the pulvinus was becoming
rudimentary and tending to disappear; and this accounts for its great
variability in structure and function.
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