26 
Lang. — Studies in the Morphology and 
tions, so that in this case photographs afford the best representation possible. 
The section in Photo. 6 passes through the second tier of the suspensor (s 2 ) 
and the hindmost portion of the hypobasal tier of the embryo (e) ; the dis- 
tinction between the two regions is brought out by the difference in size and 
appearance of the cells composing them. The section in Photo. 7 passes 
through the hypobasal tier of the embryo proper. It seems clear that the 
lower half of this (i. e. the two downwardly directed quadrants) has developed 
more than the upper half. The cells of the lower half have the characteristic 
appearance of cells of the foot. The foot thus appears to be developed 
from the hypobasal tier of the embryo proper and mainly from the two 
downwardly directed quadrants. The section in Photo. 8 passes through 
the base of the axial stele a little further forward than the root-apex ; the 
short tracheides (tr.) are seen in the stele. The section in Photo. 9 passes 
through the region of the stem-apex. The meristematic tissues show 
indications of having been derived by the segmentation of a three-sided 
initial cell, the position of which is indicated by a cross. 
It will be noted that the cells composing the portions of this last 
section above and below the meristematic region (and the same holds for the 
portions above and below the stele in Photo. 8) present the same appearance 
as the cells of the hypobasal region or foot. Thus the whole young 
shoot appears as if sunken in the basal region of the embryo. This may 
indicate that the epibasal region is partially enveloped by the hypobasal 
as the growth of the embryo proceeds. It is possible, however, that the 
cotyledon is not derived from a portion of the epibasal tier independently of 
the stem-apex, but that the apical cell of the stem is first established and the 
cotyledon derived from the first segment of this. In this case the tissue 
surrounding the apical region of the shoot would be derived from the 
epibasal tier. One or both of these explanations are required to account 
for the way in which the stem-apex and cotyledon appear sunk in the basal 
portion of the embryo. 
Four prothalli 1 were obtained with large normal embryos ready 
to grow further into young plants. These prothalli were cut into series of 
longitudinal sections, but this did not result in cutting the embryos in any 
definite corresponding plane. The embryos were all cut more or less 
obliquely, so that their interpretation from isolated sections was difficult. 
The most readily understood specimen was that of which a section is 
figured in my earlier paper. 2 This section, longitudinal as regards the 
embryo proper, was approximately median for the young shoot which was 
directed upwards. It passed through the stem-apex, which was overhung 
by the first leaf. Below the first leaf was the bulge of the young root, while 
on the other side the large foot bulged into the prothallus. The relative 
1 Cf. Ann. of Bot., vol. xvi, PI. II, Figs. 35-37. 
2 Ibid., Fig. 59. 
