278 



FOUNDATIONS OF BOTANY 



on the carbon dioxide gas which the plant absorbs, that is, 

 arranged about rather large air chambers. 



Reproduction is of two kinds, sexual and asexual, and 

 the organs by which it is carried on are complicated and 

 highly organized. An alternation of generations occurs, 

 that is, the life history of any species embraces two forms : 

 a sexual generation, which produces two kinds of cells that 



by their union give 

 rise to a new plant ; 

 the asexual genera- 

 tion, which multiplies 

 freely by means of 

 special cells known 

 as spores. 



FIG. 202. Part of Female Thallus of 

 M. disjuncta. (Enlarged.) 



fr, female receptacle ; c, cups with gemmae. 



THE STUDY OF 

 MARCHANTIA 



335. Occurrence. 



Marchantia grows on soil 

 or rocks in damp shaded places and is widely distributed. 



336. The Thallus. In general form the thallus bears some resem- 

 blance to that of some of the lichens, as Parmelia, but is plainly 

 different in color, mode of branching, and internal structure under 

 the microscope. Under the microscope (see below) the individual 

 cells may be compared with those of the medullary layer in PJiyscia. 



Note the color and general shape of the thallus and study care- 

 fully the mode of branching. The origin of the growing cells is at 

 the tip, but cells so originating afterward multiply more rapidly, so 

 that the tip comes to be in a notch. 



Viewing the thallus as an opaque object, note the diamond-shaped 

 network on the upper surface and the dot-like circle in the middle 

 of each diamond. 



Examine the under surface for (1) rhizoids and (2) scales. 



