MARCHANTIA. OOPHORE. 25 



means of transverse sections of the apex. In good median 

 longitudinal sections of the apex, note also 



1. The origin of the amphigastria, as plate-like outgrowths on 

 the ventral surface, immediately below the apex of the thallus. 



2. The formation of the air - cavities : these appear to be 

 formed by involution of the outer surface, and subsequent over- 

 arching of the cavity thus formed ; but the actual proof of this is 

 a matter of some difficulty, and requires careful cutting of sections. 



3. The development of the so-called " stomata " by division of 

 certain cells by periclinal walls. 



4. The origin of the chlorophyll-containing tissue, by budding 

 of the cells forming the floor of the young air-cavity, and frequent 

 subsequent branching. 



Similar preparations may be made from Lunularia and Fega- 

 tella with similar results : in these it is more easy to trace the 

 origin of the air-cavities. Note especially in these forms the 

 simpler structure of the " stomata," and the peculiar mucilage- 

 cells, which in Fegatella are associated in longitudinal series, and 

 attain a large size. 



Preparations should also be made to illustrate the structure of 

 the apical meristem in other forms : thus, in Metzgeria there 

 may be found a single two-sided wedge-shaped apical cell, in 

 Jungermannia a three-sided, and in Blasia a four-sided apical 

 cell. These examples will suffice to show that the type of 

 apical structure is far from being '.uniform throughout the 

 Liverworts. 



Gemmae, 



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. 



