MARCHANTIA POLYMORPHA 373 



thallus, of which they may both be regarded as 

 modifications. 



XIII. It will be well to start the study of the female 

 organs on a younger branch than that above described : 

 select a female branch which has not yet grown more 

 than a quarter of an inch in height, cut rather thick 

 transverse sections (i.e. in a horizontal plane) through 

 the head of it, mount in glycerine, and examine under 

 a low power : observe 



1. The central stalk cut through transversely, and 

 presenting characters similar to those above described. 



2. The arms, usually nine in number, radiating from 

 that central point (it may be further noted that the 

 largest gap between the arms is directly opposite the 

 morphologically upper surface of the stalk, and that in 

 this gap there is no group of archegonia) : 



3. The numerous archegonia, each of which presents 

 a circular outline from this point of view : they are 

 disposed in groups alternating in position with the arms, 

 each group being surrounded by the perichsetium. 



Under a high power the following points may be 

 ascertained 



a. That the most mature archegonia are those nearest 

 the periphery, while those of each group are succes- 

 sively younger the nearer they are to the central stalk. 



I. That each mature archegonium as seen in section 

 consists of a wall (one layer of cells in thickness) 

 which surrounds and incloses a large, naked, nucleated 

 ovum. 



XIV. Cut vertical sections through a female branch 

 of like age to the above : treat as before, and observe in 

 median sections 



