388 



BOTANY. 



spores, while the interior ones contain microspores. Both macrospcrea 

 and microspores are produced in <jreat 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 



Ji 



Fig. 280. Germination of the microspores of Isoftes lacustris. A, amicrospore, 

 side view. B, the same, ventral view ; the spore contents have divided into a few 

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

 ventral, and <J rf the dorsal cells. C, a side view of microspore ; the four cells, Q ft t 

 6, 6, have disappeared, and spermatozoids have formed. D, ventral view of C; a to 

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



which there are from forty to fifty or more, all belong to the single 

 genus Isoetes;* we have representations of about fourteen within the 

 United States. 

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



* The North American species of Pteridophytes are well described 

 in "Our Native Ferns and their Allies," by L. M. Underwood. (Holt, 



1888.) 



