388 



BOTANY. 



spores, while the interior ones contain microspores. Both macrospcres 

 and microspores are produced in great numbers iti the sporanojia. 



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

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



Mg. 980. — Germination of the' microspores of laoetes lacitsfris. A, a microapore. 

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

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

 ventral, and J rf the dorsal cells. C, a side view of microspore ; the four cells, 8 R 

 6y 6, have disappeared, and spermatozoids have formed, i?, ventral view of C ; a to 

 /, development of spermatozoids. « and/ X 700, the others X 580,— After Millardet. 



which there are from forty to lift^' or more, all belong to tlie single 

 genus Isoetes; we have representations of about fourteen within the 

 United States. 

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



