1 8 ENGELMANN—THE GENUS ISOETES IN N. AMERICA. [375 
14. I. Nuttallii. 
II. Trunk trilobed, numerous stomata and bast-bundles in the quadrangular 
leaves; velum partial. 
15. /. Cubqna. 
§ p. Geographical Distribution. 
Only a small part of the North American continent has been Well ex¬ 
plored for Isoetes, and there, from Massachusetts to the Chesapeake Bay, 
tthey appear abundant enough ; farther south, and in the whole interior 
and western part of the continent, they have thus far been found only in 
a few localities. Some species are quite local, as is the case also with 
many species of the old world, while others are widely distributed. Our 
two northern species are identical with, or closely allied to, Europeari 
forms, all the others are quite distinct from such, so that there is scarcely 
more than a generic analogy between the species of our middle and 
southern regions with the Mediterranean ones or those of other regions 
of the globe. 
The old Linnean Isoetes lacustris is the only species which has been 
found to extend from the Atlantic to the Pacific States, and it probably 
occupies a northern belt of the northern hemisphere, though it seems 
mot to have been discovered as yet in Asia. The American forms allied 
to I. echinosfora, the other North European species, are the most com¬ 
mon in the belt of northern States as far west as Michigan, and have been 
•detected also on the western slope of the Rocky Mountains. Of the others, 
/. Bngelmanni extends from Massachusetts to Georgia and westward to 
Missouri, though thus far not found anywhere else west of the Alleghany 
Mountains. 1 . Jlaccida is peculiar to Florida and I. B&larideri to the 
lakes of the western mountain chains, the Rocky Mountains as well as 
the Sierra Nevada. /. melanopoda occupies parts of the Mississippi val¬ 
ley from Central Illinois to Northeastern Texas, while I. Nuttallii is the 
only species found in the valley of the Columbia river. All the other 
species seem to be nearly or quite local, I. pygmcea , in the Californian 
Sierra, but most of them on the Atlantic border; thus I. Tuckermani oc¬ 
curs only near Boston, /. sacckarata on streams emptying into the Chesa¬ 
peake Bay, and I. melanospora only on that peculiar and, botanically, so 
interesting rock, the Stone Mountain of Georgia. Some species which 
seemed local have lately assumed a little wider range, though yet quite 
restricted; among these I mention I. rip aria oi the banks of the lower 
Delaware river, which occurs also farther north, and T. Butleri , first 
known only from the Indian Territory, now also found in Tennessee. 
There can be no doubt but that some of the apparently local species will 
yet be found in a more extended area, when botanists will include in their 
researches these obscure and inconspicuous plants. 
From the warmer parts of North America we know only /. Cubana y 
from Cuba; none have yejt turned up from Mexico. 
The following table will explain itself. 
0 1 2 3 4 5 6 7 8 9 10 
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