200 



STUDIES IN CRYPTOGAMS 



The sterile shoots, Fig. 369, st, appear much later in the season. 

 They give rise to repeated whorls of angular or furrowed branches. 

 The leaves are very much reduced scales, situated at the internodes. 

 The stems are provided with chlorophyll and act as assimilating tis- 

 sue, nourishing the rhizome and the fertile shoots. Nutriment is also 

 stored in special tubers developed on the rhizome. 



369. Equisetum arvense; st, sterile shoot;/, fertile shoot showing the 

 spike at a; b, sporophyll, with sporangia; s, spore. 



Other species of equisetum have only one kind of shoot — a tall, 

 hard, leafless, green shoot with the spike at its summit. Equisetum 

 stems are impregnated with silica and they are sometimes used for 

 scouring floors and utensils: hence the common name "scouring rush." 



ISOETES 



Isoetes or quillworts are usually found in water or damp soil on 

 the edges of ponds and lakes. The general habit of a plant is seen 

 in Fig. 370, a. It consists of a short, perennial stem bearing numer- 

 ous erect, quill-like leaves with broad sheathing bases. The plants 

 are commonly mistaken for young grasses. 



Isoetes bears two kinds of spores, large roughened ones, the macro- 

 spores, and small ones or microspores. Both kinds are formed in spo- 



