Hollo way. — Prothallus, &c, of Tmesipteris. 



401 



young embryo figured in longitudinal section in the present paper in the 

 series figs. 47a to 47d possesses an apical cell from which segments have 

 apparently already been cut off. In the series figs. 48a to 48f another 

 embryo, at a slightly older stage of development, is given in longitudinal 

 section which apparently possesses two apical cells, one in each epibasal 

 quadrant. In these early stages it is not clear whether or not the cells 

 alongside the apicals have actually been cut off from them as segments 

 or have arisen simply by the general segmentation of the quadrants. In 

 those figured the former seems to be the case, and the apicals are strongly 

 defined Until the shoot has reached the size when the overlying pro- 

 thallial tissues are ruptured, the apical cell usually cuts off more segments 

 towards the base than towards the apex of the embryo. That illustrated 



Figs. 47a-47d. 



-Embryo in longitudinal section, showing initiation of the apical 

 cell and also the main divisions. X 100. 



in fig. 48 is not cut medianly for foot and shoot together. The full size 

 of the former appears at the beginning of the series, but of the latter in 

 the sections marked D and E. The section F, which shows the neck of 

 the archegonium, lies five sections beyond that marked E. In fig. 49 

 another embryo is shown in which the single apical cell has been functioning 

 for only a short time. The. position of this embryo in the transverse section 

 of its parent prothallus is shown in fig. 50. A median longitudinal section 

 of another such embryo, with the foot rather more developed, is given in 

 fig. 51. In all these the basal wall and the first inclined walls in both 

 epibasal and hypobasal regions can be distinguished. They illustrate also 

 the beginning of the outgrowth of the superficial cells of the foot, and in 

 fig. 49 the cell-divisions in the prothallial tissue abutting on the foot can 

 be well seen. 



