444 ELEMENTARY BIOLOGY. [CHAP. 



tion of adventitious buds. The latter are produced singly 

 on the dorsal side of the leaf-stalks, near the base. 



The attachments of the fronds are nodes, the spaces 

 between two such successive attachments, internodes. It 

 will be observed that the internodes do not become crowded 

 towards the free end, and there is nothing comparable to 

 the terminal bud of Chara with its numerous rudimentary 

 appendages. 



When the fronds 'have attained their full size, the edges 

 of the pinnules will be observed to be turned in towards 

 the underside, and to be bordered by a fringed membrane 

 called the indusium, which roofs over the groove enclosed 

 by the incurved edge. At the bottom of the groove brown 

 granules are aggregated in large numbers, so as to form a 

 streak along each side of the pinnule. The granules are the 

 sporangia, and the streaks formed by their aggregation, the 

 sori. 



Examined with a magnifying glass, each sporangium is 

 seen to be pouch-shaped, like two watch-glasses united by 

 a thick rim. When ripe, it has a brown colour, readily 

 bursts, and gives exit to a number of minute bodies which 

 are the spores. 



The plant now described is made up of a multitude of 

 cells, having the same morphological value as those of 

 Chara, and each consisting, at least when young, of a pro- 

 toplasmic mass, a nucleus and a cellulose wall. These cells, 

 however, become very much modified in form and structure 

 in different regions of the body of the plant, and give rise 

 to groups of structures called tissues, in each of which the 

 cells have undergone special modifications. These tissues 

 are, to a certain extent, recognizable by the naked eye. 

 Thus, a transverse section of the rhizome shews a circum- 

 ferential zone of the same dark-brown colour as the external 



