MARCHANTIA POLYMORPHA 371 



cubical form, and small size, which together constitute 

 a dense central mass. 



Trace the channel of one of the flask-shaped cavities 

 up to the surface of the thallus, and note that the 

 structure of the pore is quite distinct and different from 

 that of the "stoma." 



Compare antheridia of various ages in sections cut from 

 younger male branches : by such a comparison it may be ascer- 

 tained that each antheridium arises from a single cell at the base 

 of the flask-like cavity : trace the successive divisions which 

 accompany the development of one such single cell into the 

 mature antheridium. 



Cut tangential sections from the upper surface of a male branch, 

 and under a high power note 



a. The " stomata," of similar character to those on the vegetative 

 thallus. 



b. The pores or openings of the cavities in which the antheridia 

 are seated. These pores are of about the same size as the 

 " stomata," but differ from them in being often triangular, and in 

 the number (nine) and arrangement of the surrounding cells. 



Cut median longitudinal sections of a thallus of Pellia on which 

 antheridia are borne (see p. 362) : the antheridia are mature in late 

 spring or early summer, and will be found in various stages of 

 development in material taken in the early part of the year. 

 Examine the sections with a low power, and the antheridia will be 

 readily seen, having a form and structure similar to those of 

 Marchantia : each is seated singly, in a flask-like depression of 

 the upper surface of the thallus, and covered over by a circular lip, 

 which projects beyond the general surface of the thallus, and is 

 traversed by a very narrow pore : through this the spermatozoids 

 escape. 



Similar sections cut through the apex of a thallus taken in 

 spring, will show antheridia in various stages of development, 

 and will demonstrate that, as in Marchantia^ each originates from 

 a single superficial cell of the upper surface of the thallus. 



B B 2 



