MARCHANTIA. OOPHOKE. 27 



temperature, and exposed to the light : on examining 

 them after five or six days, they will be seen to be 

 elongated transversely to their original axis of growth, 

 the base of each of the lateral indentations serving as 

 an organic apex : from the lower surface root-hairs have 

 been formed, by simple outgrowth of single cells. After 

 growth has been continued for a longer time the 

 differentiation of tissues characteristic of the mature 

 thallus, with " stomata " and air-cavities, becomes appa- 

 rent on the upper surface, the thallus thus assuming 

 a dorsiventral character. 



The Male Branch (Anther idiophore). 



IX. Having noted the general form of the male 

 branch of the thallus, with its stalk and terminal disk, 

 cut transverse sections of the stalk, mount in glycerine, 

 and examine under a medium power. Observe 



1. The circular outline of the sections. 



2. Two involutions of the margin, corresponding to 

 two channels, which traverse the stalk longitudinally : 

 due investigation will show that these are on the 

 morphologically lower face of the stalk. 



3. Rhizoids will be found traversing these channels 

 longitudinally. 



4. The tissues seen in these sections are not clearly 

 differentiated. 



X. Cut median vertical sections through the terminal 

 disk : mount in weak glycerine, and examine first under 

 a low power : observe 



1. The general outline of the section, and especially 

 the attachment of the disk, and the flat upper surface. 



