ENGELMANN — THE GENUS ISOETES IN N. AMERICA. 369 



are called microsporangia. Almost all the species are monoe- 

 cious, bearing macrosporangia on the base of the outer and 

 microsporangia on that of the inner leaves. I am not awai"e that 

 any exotic species behave differently, but here w^e have two spe- 

 cies vvrhich 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 dioecious, 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 

 /. melanopoda I have sometimes seen leaves with microsporangia 

 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 lower 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 / 

 Tuckermani) or are smoother than that (often in /. melanopoda). 

 To examine the spores well 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 

 100 to 150 diameters is necessary. With the aid of this we find 

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

 small and mostly somewhat depressed, distinct or sometimes 

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

 lanospora, Butleri, and Ntittallii. 



3. With larger, broader tubercles, generally more distant and 

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

 /. Jlaccida, ??ielanopoda, and Cubana. 



3. With tubercles elongated into spines ; these are simple and 

 very fragile, or here and there confluent and forming sometimes 

 short crests : /. echinospora and its forms. 



iv — 2 — 12 



