3 lhe 
OUR AMPHIBIOUS PERSICARIAS a1L 
without the other, is hopelessly illogical on the basis of characters 
as they are outlined in our books. Neither of these plants have by 
virtue of their descriptions in all our common books any better 
reason for existence or acceptance, than any of the number pub- 
lished by Dr. Greene, and most of his have been based on more 
solid distinctions than those of these two plants. Admitting for 
example as we must, that P. emersa Michx. has an aquatic phase 
that the manuals can not distinguish from P. amphibium Linn., 
then there is nothing left of all the descriptions of all the manuals, 
except that the former is usually broader-leaved and usually 
longer spiked P. amphibium. P. Hartwrightu is for similar reasons 
but a P. amphibium with spreading borders to the ochrea. 
The ecology of the amphibious persicarias is to be taken into 
consideration in their classification. When we force certain plants 
into abnormal habitats producing peculiar individuals these 
changed “‘forms’’ are in no way to be considered as new species 
or for that matter even as “‘varieties.’’ Plants, however, naturally 
choose their own habitats or at least adapt themselves to them. 
If we find zm one locality a plant like P. fluitans which takes always 
to deep water,—and another like P. ammophila which though 
early in the season possesses leaves like those of P. fluwitans, but, 
unlike it, can not be made to bloom except in the terrestrial phase 
when the aquatic part of the plant has almost disappeared, and 
which will never bloom except out of water, and if this character 
is found to be constant, then we are justified in saying that the 
plants are not the same. It may be said that they are but two 
“forms” that have adapted themselves to different habitats. 
It is to be remembered that these habitats are not only near 
one another but actually continuous or contiguous. Seasonal 
drought and freshet changes may have brought about an inherent 
disposition to take to one prevailing habitat or other, and this 
tendency may have been inherited in succeeding generations. 
At all events the finding of a specimen of P. ammophila with shoots 
blooming in the aqautic phase or, vice versa, of a blccming shoot 
of terrestrial P. fluitans would sufficiently establish the identity 
of the two species. Such have not as yet been found and I there- 
fore prefer to regard them as separate species until their identity 
has been proved. 
_ That there is a factor to be explained by ecologists beside 
the mere differences in the above-mentioned plants, 7. e., P. 
