2 90 PHARMACEUTICAL BOTANY 



In some varieties the fruiting cone is borne on the ordinary 

 stem, in others on a special stem of slightly different form. In the 

 latter the spores are provided with elaters, which, being hygroscopic, 

 coil and uncoil with increase or decrease in the amount of moisture 

 present, thus aiding in the ejection of spores from the sporangia. 

 The number of species is small and included under one genus, 

 Equisetum. (See fig. 158.) 



SUBDIVISION III. 



The group Filicineae is the largest among the vascular cryptogams 

 and includes all the plants commonly known as Ferns. The main 

 axis of a typical fern is a creeping underground stem or rhizome 

 which at its various nodes bears rootlets below and fronds above. 

 These fronds are highly developed, each being provided with a 

 petiole-like portion called a stipe which is extended into a lamina 

 usually showing a forked venation. Some ferns possess laminae 

 which are lobed, each lobe being called a pinna. If a pinna be 

 further divided, its divisions are called pinnules. The unfolding of a 

 frond is circinate and it increases in length by apical growth. On 

 the under surface of the laminae, pinnae, or pinnules may be seen 

 small brown patches each of which is called a sorus, and usually 

 covered by a membrane called the indusium. Each sorus consists 

 of a number of sporangia (spore cases) developed from epidermal 

 cells. In some ferns the entire leaf becomes a spore-bearing organ 

 (sporophyll) . Most sporangia have a row of cells around the margin, 

 the whole being called the annulus. Each cell of the annulus has a 

 U-shaped thickened cell wall. Water is present within these cells and 

 when it evaporates it pulls the cell walls together, straightening the 

 ring and tearing open the weak side. The annulus then recoils and 

 hurls the spores out of the sporangium. Upon coming into contact 

 with damp earth each spore germinates, producing a green sep- 

 tate filament called a protonema. This later becomes a green heart- 

 shaped body called a prothallus. It develops on its under surface 

 antheridia or male organs and archegonia or female organs as well 

 as numerous rhizoids. Within the antheridia are developed motile 

 sperms, while ova are produced within the archegonia. The many 

 ciliate sperms escape from the antheridia of one prothallus during a 



