ZD PKACTICAL BOTANY. 



2. The ordinary chlorophyll-parenchyma of which it 

 is mainly composed. 



3. Superficial hyaline cells, from which the rhizoids 

 are subsequently derived. 



4. The single cells containing oil-hod ies. 



It may further be observed that the gemma is in its 

 peripheral part only one layer of cells in thickness, 

 while the central part is a solid mass : also that the 

 structure is alike on both sides of the gemma, i.e. that 

 it does not as yet show any trace of a dorsi ventral 

 character. 



VIII. Cut transverse sections of a thallus so as to pass 

 through the middle of one of the cups : mount in very 

 weak glycerine, or in water, and examine under a low 

 power : note 



1. The two lips of the cup, which appear as out- 

 growths from the upper surface of the thallus, and show 

 more or less clearly the same structure, especially in 

 the lower part. 



2. The numerous gemmae, in various stages of deve- 

 lopment, which are attached to the base of the cup by 

 unicellular stalks. 



3. Unicellular outgrowths or hairs, with mucilaginous 

 walls. 



Trace under a high power the process of development of the 

 gemma. It may be seen that the gemma originates as a unicellular 

 papilla, which divides first into two cells: the lower remains 

 quiescent as the unicellular stalk, while the upper cell grows and 

 divides, ultimately giving rise to the mature gemma. Trace the 

 succession of cell-divisions by comparison of gemmse of various 



Removing some gemmae from the cups, germinate 

 them on clean moist sand under a bell-glass at a medium 



