MARCHANTIA POLYMORPHA 367 



cell, which is, however, only one of a series of initial cells of 

 like form, as may be ascertained on careful investigation by 

 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 : the usual tests for mucilage should be 

 applied (see p. 94). 



Preparations should also be made to illustrate the structure of 

 the apical meristem in other forms : Hetzgeria furcata will be 

 found to be an excellent object for this purpose. It is commonly 

 found growing on damp rocks, tree trunks, &c., especially in 

 mountain districts. In order to see the single two-sided, wedge- 

 shaped apical cell, fresh or hardened material is to be treated 

 till quite transparent with " eau de javelle," and mounted in 

 glycerine : in apices thus treated the apical cell and its segmenta- 

 tion, as well as the dichotomous mode of branching of the thallus 

 may be readily seen. In Jungermanma there is 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. 



