KNGELMANX — THE GENUS ISOETES IN N. AMERICA. 369 



are called microsporang-ia. Almost all the species are monce- 

 cious, bearing macrosporangia on the base of the outer and 

 microsporangia on that of the inner leaves. I am not aware that 

 any exotic species behave differently, but here we have two spe- 

 cies which deviate from this norm. /. melanopoda in Illinois as 

 well as in the Indian Territory, from both of which localities I 

 have examined several hundreds of specimens, is polygamous, 

 i.e. monoecious as well as dicecious, and shows about an equal 

 number of male, female, and monoecious plants. The allied /. 

 Butleri is apparently always dioecious, no monoecious plants 

 having been discovered among about one hundred examined. In 

 II melanopoda I have sometimes seen leaves with microsporancria 

 irregularly interspersed among those that bear macrosporangia. 

 The macrospores are little spheroid bodies between one-fourth 

 and three-fourths of a millimeter in diameter. Their surface is 

 divided by a circular rim in a low^er hemispherical and an upper 

 three-sided pyramidal part, the three faces of which consist of 

 spherical triangles and are separated from one another by three 

 elevated ridges. The crusty surface of these spores, chalky-white 

 or whitish in most species and dusky (when wet black) in /• 

 melanospora^ is rarely smooth, but generally sculptured and 

 differently marked. The three upper triangles are sometimes 

 marked differently from the lower hemisphere (especially in / 

 Tuckermant) or are smoother than that (often in Z melanopoda). 

 To examine the spores w^ell it is necessary to soak the leaf-base, 

 carefully remove some of the wet spores and let them dry on the 

 slide, for they must be examined dry, and best under a power of 

 50 or 60 diameters ; but, to study the sculpture well, a power of 

 to isO cJiameters is necessary. With the aid of this we find 



GO 



the macrospores — i. Minutely tuberculated or warty; the warts 

 small and mostly somewhat depressed, distinct or sometimes 

 somewhat confluent, in /. pygmcea^ Bolanderi^ saccharata^ me- 



Nu it alia 



w 



distinct, but also here and there confluent, worm-like ; thus In 



Ji< 



With 



very fragile, or here and there confluent and forming sometimes 

 short crests : /. eckinospora and its forms. 



IV — 2 — 12 



f 



