62 ELEMENTARY BIOLOGY. [CHAP. 



free germinate; the product of that germination is the incon- 

 spicuous and simply cellular prothallus; an independent 

 organism, which nourishes itself and grows, and on which, 

 eventually, the essential organs of the sexual process the 

 archegonia and antheridia are developed. 



Each impregnated embryo cell produces only a single 

 'fern,' but each 'fern' may give rise to innumerable pro- 

 thallia, seeing that every one of the numerous spores de- 

 veloped in the immense multitude of sporangia to which the 

 frond gives rise, may germinate. 



LABORATORY WORK. 



A. THE FERN-PLANT; ASEXUAL GENERATION. 

 a. External characters. 



a. The brown underground stem or rhizome, with 

 a lighter band (the lateral line) running along 

 each side of it : its nodes and internodes. 



b. The roots springing from the rhizome. 



c. The leaves or fronds arising from the rhizome at 

 intervals, along the lateral lines. 



a. The great amount of subdivision of the frond : 

 its main axis (rachis) ; the primary divisions or 

 pinna; the ultimate divisions or pinnules. 



/?. The sori ; small brown patches along the 

 margin of the under surface of some of the 

 pinnules. 



d. The nodes and internodes of the rhizome. The 

 absence of a terminal bud on it. 



