12 ENGELMANN—TIIE GENUS ISOETES IN N. AMERICA. [369 
are called micro sporangia. 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 aware that 
any exotic species behave differently, but here we have two spe¬ 
cies which deviate from this norm. I. 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 I. 
Butleri is apparently always dioecious, no monoecious plants 
having been discovered among about one hundred examined. In 
I. 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 diarpeter. 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 I. 
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—x. Minutely tuberculated or warty; the warts 
small and mostly somewhat depressed, distinct or sometimes 
somewhat confluent, in I. pygmcea , Bolanderi , saccharata , me¬ 
lanospora, Butleri , and Nuttallii. 
2. With larger, broader tubercles, generally more distant and 
distinct, but also here and there confluent, worm-like; thus in 
I. Jlaccida , melanopoda , and Cubana. 
3. With tubercles elongated into spines ; these are simple and 
very fragile, or here and there* confluent and forming sometimes 
short crests: I. echinospora and its forms. 
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