280 MR. J. R. VAIZEY ON THE ANATOMY AND 
the exomeristem. The endomeristem differs from the exome- 
ristem by dividing equally throughout in any transverse plane, 
so that all the cells in a given plane are of the same age. The 
epidermis in the sporogonium is not derived from any special 
layer or meristem, but is only the most external layer of cells of 
the exomeristem. 
Figs. 6, 7, 8 a-d, represent the external morphology at various 
stages, from the youngest I have been able to obtain (a small . 
fusiform embryo) to the nearly mature sporogonium with fully 
developed theca. At the earliest period the embryo grows by 
means of an apical cell (fig. 32); but from the stage repre- 
sented by fig. 6 b, or very shortly after, the apical cell is 
divided up into several cells, and growth in length is no longer 
continued by new segments being cut off from an apical cell. 
At a certain period after this stage is reached, the formation 
of the theca commences (fig. 8a); this is seen in the slight 
swelling which appears a little below tbe apex. This swelling is 
greatest at its most distant point from the apex, forming first 
what will eventually become tbe apophysis. At a later period 
the upper part swells, and develops further to form the 
sporangium. 
About this time—the stage shown in fig. 8 5—the young stomata 
begin to be formed. They are formed by given cells at the sur- 
face ceasing to divide, but continuing to increase in size at the 
same rate as the surrounding cells, thus forming mother-cells for 
stomata, which are about eight times the size of the surrounding 
superficial cells. The nucleus of the mother-cell divides tan- 
gentially, and a radial wall is formed between the two daughter- 
nuclei, connecting the external peripheral wall with the internal 
central wall of the mother-cell by a plate of cellulose. It, 
however, does not extend to any of the other walls of the cell*. 
At a later period this cell-plate splits, thus forming the opening 
ofthestoma. Both the nuclei remain, and can be seen throughout 
the life of the sporogonium. 
It is found that in the theca the endomeristem is more largely 
developed in proportion to the exomeristem than in the seta. 
Compare figs. 48 and 40. 
* In Funaria, according to Haberlandt (6), the development of the stcma is 
different, and there is in that form a stage at which the two guard-cells are 
completely separated, parts of the cell-wall separating them being dissolved 
subsequently. 
