192 PRACTICAL BOTANY 



lowest cell of each tier projects into the cavity of the " stoma," 

 so that the channel at that point presents a stellate appearance 

 in surface view. 



V. Remove a number of the rhizoids : mount them in water 

 or glycerine, and examine under a low power : two types of 

 these elongated unbranched hairs may be recognized 



a. Those with smooth walls : these are the more numerous : 



b. Those with peg-like projections of the wall into the cavity 

 of the hair : the protoplasmic contents are very scanty. 



Gemmcs. 



VI. 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, 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 sub- 

 sequently 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. 



VII. 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 outgrowths 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 development, 

 which are attached to the base of the cup by unicellular stalks. 



3. Two involutions of the margin, corresponding to two 

 channels, which traverse the stalk longitudinally. 



