1903] Eaton,— Three New Varieties of Isoetes 279 
of a different appearance and conclusions regarding them were held 
back until further investigation. 
During the past summer I have been so fortunate as to find an 
abundance of this form at Watson’s Pond in Taunton, in Mulberry 
Meadow Brook in Easton, and Winneconnet Pond, Norton. Its 
characters are the same in all respects as in Robbins’ plants. 
Although offering several important differences it is quite closely 
related to 7. Canadensis (Engelm.) A. Br. and would best be con- 
sidered a variety of that species. In recognition of the fact that its 
first recorded collection in America was by one of the best New 
England collectors of his day I propose to name it 
I. CaNapENsrS, var. Robbinsii. Trunk bilobed, 8-15 mm. long: 
leaves, 15-30, 10-38 cm. long, 1—1.5 mm. wide, dark green, very rig- 
idly erect both in water and out, fine-pointed, with stomata and 4 
bastbundles: velum } to 4 or more indusiate: sporangia covered 
with brown sclerenchyma cells; gynospores 450-600 p, very thickly 
beset with anastomosing jagged walls (much as in Z. riparia): 
androspores 28.7-32.8 p in long diameter, rough or slightly papil- 
lose or with a few tubercles. 
This variety differs from Z. Canadensis principally in its rigid 
habit, broader velum, densely sclerenchymatous sporangia, and the 
dense sculpture of the spores, which strongly resemble those of Z. 
riparia. 
Uxbridge, Massachusetts, “in rather sandy still part of a small 
stream, leaves ten, 1o inches high, very finely and sharply pointed ” 
Robbins, 1831; Millpond, Uxbridge, 1845 and 1864, Robbins: 
_ Easton, Mulberry Meadow River, Aug. 16, 1903, 4. A. Eaton; 
Norton, Winneconnet Pond, 4. A. #.; Taunton, Watson’s Pond, 
A.A. E., type. Robbins’ specimens were evidently a source of much 
uncertainty to Dr. Engelmann. One was annotated as follows: 
“ Tuckermanni? riparia? Braunü? apparently /acustris, T. riparia?” 
Another is annotated “riparia major” and “lacustris maxima.” 
They were all finally included in Z. riparia. 
The aspect of this plant is very much like that of 7. Engelmanni, 
especially when growing out of water. When submersed the leaves 
are rigidly erect and look much like those of some junci. The bulb 
and leaf bases so far as covered by the mud are apt to be pinkish 
or cream colored. The variety approximates the terrestrial habit 
fully as much as Z7. Enge/manni, being found on the border of shal- 
low brooks and near the upper limit of water in ponds. 
