388 



BOTANY. 



spores, while the interior ones contain microspores. Both macrospcrea 

 and microspores are produced in great numbers in the sporangia. 



The Quillworts are for the most part aquatic plants ; they are found 

 chiefly in the north temperate and warm regions. The species, of 



Pig. 280. Germination of the microspores of Isoetes lacustris. A , a microapore, 

 Bide view. S, the same, ventral view ; the ppore contents have divided into a few 

 cells, of which v in each figure represents the rudimentary prothiillium ; ^ ft are the 

 ventral, and rf <? the dorsal cells. C, a side view of microstore ; the four cells, ^ ; 

 i t d, have disappeared, and spermatozoids have formed. D, ventral view of C\ a to 

 /, development of spermatozoids. e and/ X 700, the others x 580. After Millardet. 



which there are probably a dozen or more, all belong to the single 

 genus Tsoetes; we have representatives of eight or ten withiu the 

 United States. 

 Two species of Isoetes occur as fossils in the Tertiary (Miocene). 



