368 PKACTICAL BOTANY 



Gemma. 



VII. Remove from one of the cups on the upper 

 surface of the fresh thallus of Marchantia some of the 

 gemmae : mount them in water, and note under a low 

 power 



1. The flattened disk-like form of the gemma, pre- 

 senting a nearly circular outline, with two lateral 

 indentations, and a scar at the base where it was 

 attached to the thallus which produced it. 



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-bodies. 



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 dorsiventral 

 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 de- 

 velopment, which are attached to the base of the cup 

 by unicellular stalks. 



