1896. | Isoetes riparia and I, saccharata. 223 
pear from Engelmann’s account. Yet there appears to bean 
unmistakable specific distinction. The widely varying velum 
of. riparia (from quite narrow to three-fourths the sporan- 
gium), and its spores differing so remarkably in size and mark- 
ings, as well as the varying habit of growth and gradations of 
color; and the wide departures from the type in point of size, 
tolor and spore characters in J. saccharata may well cause 
doubt at times as to individual plants. But the narrow velum 
of the latter seems to be a constant feature, while in /. riparia 
itvaries from leaf to leaf of the same plant. This single defi- 
tite character, constant in the most aberrant forms, seems to 
me to gather significance as other characters vary, until it 
becomes as it were a touchstone. Moreover, until dioecious 
tendencies are made out in I. saccharata there is good rea- 
Son for specific distinction. 
Media, Pa. 
