1896, ] Isoetes riparia and I. saccharata. 219 
I. riparia Engelm.—A larger plant with slender but rather 
rigid deep green leaves (about fifteen to thirty in number) four 
to eight inches long, rarely longer; stomata numerous, dis- 
sepiments_ thick, consisting of about four layers of cells; 
sporangium mostly oblong, distinctly spotted by groups of 
brown sclerenchym cells, one-fourth or rarely one-third of it 
0.028 to 0.032™" long. 
It is to be remarked that few hard and fast contrasts are es- 
tablished in the above descriptions. A difference of color, a 
larger size, a larger number of leaves are not such items as, 
will help greatly to determine the allegiance of any doubtful 
plant in hand, Spore characters alone seem definite. (The 
relative sizes of the microspores are made a good deal of by 
Engelmann.) The sporangia of both are spotted, though 
akind of distinction is for some reason attempted in Gray's 
Manual, 6th edition, where the sporangium of J. saccharata is 
stated to be “nearly unspotted.” : 
Biologically, so far as known and studied, the two species 
have been thought quite similar. j i 
_ VARIATIONS, —l. riparia. My acquaintance with this spe- 
nes, as it occurs on the Delaware near Chester, Pa., and im- 
mediately Opposite on the New Jersey shore, extends over 
fe years. ... It confines itself to clay-gravel tidal banks 
Which are Capped either with mud or fibrous growths that 
event the spores being washed away by the storm-tides. 
large number of plants gathered in August, 1894, showed 
Faudlority with all mature leaves decidedly longer than the 
‘mit given, The usual, not the occasional, length was nine 
and three-fourths to ten inches. The color was dark green. 
The bulb r crown, when carefully measured, was found to be 
one-half to five-eighths of an inch in diameter. The sporangia 
= oblong, 4 to 5™" long. The velum covered two-thirds to 
rths of the sporangium, instead of but one-third. 
the Macrospores were of the usual size, 0.50 to 0. 63 : | 
hi Ndges quite jagged, and more or less reticulate : 
the = fathering these plants I noticed many, only Ps et 
ag Which seemed to have lost their outer leaves, if : ig 
sie macrosporangia. Only those plants were collected, 
