ACROGENS, OR FLOWERLESS PLANTS. 



69 



589. The reproductive organs of flowerless plants vary ac- 

 cording to the tribes of that division of the vegetable kingdom ; 

 and have so little relation to each other, that each principal 

 tribe may be said to have its own peculiar method of propaga- 

 tion. 



590. They all agree in their reproductive parts or spores, 

 which are analogous to seeds, not germinating from any fixed 

 point, but producing root or stem indifferently from any point 

 of their surface. This germination is therefore vague. 



591. The principal tribes are Ferns (592), Mosses (598), 

 Lichens (605), Algacea (607), and Fungacea (610). 



592. FERNS are increased by, little bodies, called spores, 

 enclosed within cases named tliectz or sporangia 302 303 , which 

 often grow in clusters or sori 3M , from the veins of the under 

 sides of the leaves, or from beneath the epidermis. The latter, 

 when it encloses the thec<e, is termed the indusium 308 . 



593. The indusium separates from the leaf in various ways, 

 in consequence of the growth of the thecse beneath it. 



594. The thecse have frequently a stalk which passes up 

 one side, and finally, curving with their curvature, disappears 

 on the opposite side 307 . 



595. The part where the stalk of the theca is united with 

 its side, is called the annulus. 



