THE HIGHER CRYPTOGAMIA. 165 



of the outermost layer of the latter, abound with a saturated 

 solution of dextrine, in which the nucleus floats in the form 

 of a very sharply defined vesicle with less highly refractive 

 contents. 



During the secretion of the exosporium, the walls of 

 those cells which are adjacent to the columella towards the 

 apex of the fruit assume a deep-brown colour. It is in 

 these cells that the partial disruption of the theca com- 

 mences, by means of which the spores, which in the mean 

 time have fully ripened, become free. 



In Gymnostomum pyriforme, the multiplication of the 

 cells of the upper part of the spindle-shaped rudiment of 

 the fruit extends downwards far beyond the base of the 

 future fruit. In this way an apophysis originates, which in 

 the earliest stages of development far exceeds the fruit in 

 size. After the separation of two annular layers of cells 

 beneath the apex of the rudimentary fruit, by which means 

 the vacant space between the outer and inner wall of the 

 theca is formed, individual cells of the inner side of the 

 outer wall grow so as to form chains of cells, the uppermost 

 of which remain in connexion with the upper surface of the 

 inner waU (PI. XXII, fig. 7). 



In the very young capsule of Gymnostomum pyri- 

 forme, at the time of the division of the cells which 

 adjoin the outer and inner sides of the primary 

 mother-cells, the latter have the form of very flat plates 

 parallel to the axis of the fruit (PI. XXII, fig. 8). During 

 the further development of the theca, the transverse dia- 

 meter of these cells increases considerably. A proportion- 

 ably large nucleus with a large nucleolus becomes visible, 

 floating freely in the fluid contents (PL XXII, figs. 9, 10). 

 The length of the cell soon considerably exceeds its height 

 and width. 



At this time two new globular nuclei appear in the place 

 of the vanishing primary nucleus (PL XXII, fig. 11). Half 

 of the granular mucilaginous cell- contents accumulates 

 round each of them; two globular masses of protoplasm 

 are formed, which, after secreting cellulose over their entire 

 surface, constitute the free spherical mother-cells of the 

 spores (PL XXII, fig. 12). 



