202 AMERICAN MIDLAND NATURALIST 
out been known in Europe for centuries. Linnaeus knew of the 
fact, and was sure of it—possibly by his own observation—when 
he called the plant amphibium. 
As to P. Hartwrighti1, A. Gray, who recognized it as a separate 
species, doubtless knew of the plant in both an aquatic and a 
terrestrial phase, or if he did not know it in the former he ccriainly 
knew it to be different from any corresponding phases of any 
plants known up to his time. Had any novice or amateur written 
to him that P. amphibium changed to P. Hartwrightu, he weuld 
have at once perceived in it the mere guess. of some blundering 
tyro, ignorant of the fact that more then one species is dimorphic, 
or even polymorphic, and incompetent to distinguish two species 
by their respective descriptions. 
An opinion regarding the status of the amphibious Persicarias 
different from those of the New England as well as the New York 
botanists is that of Dr. E. L. Greene, who first took up the logical 
segregation of these plants. The groups into which they fell 
under his treatment may be designated as the Hartwrightianae, 
the Emersae, and the Amphibiae. The last I should prefer to omit 
and distribute its members between the other two. 
Dr. Greene maintains that a number of valid species have 
been overlooked hitherto, or referred to the three above mentioned 
species. On the basis of specific distinctions usually in vogue 
among botanists at present for other plants as a standard, one can 
hardly hesitate in agreeing with him. True, the same standards 
for segregation can not always be applied to all plants indes- 
criminately, still it is inconsistent and illogical to neglect princi- 
ples of differentiation in one case and apply them in another 
when the cases themselves are undoubtedly similar. Dr. Greene 
has besides devoted to this class of plants more study, particularly 
in the field where alone they can be scientifically known, than any 
other American botanist. His conclusions regarding them therefore 
ought at least to be considered with some regard rather than 
with the total indifference of botanists generally. As I have 
already shown he is the first of our modern phytographers to 
describe and insist on describing these polymorphic plants with . 
different paragraphs for the phases which are as different as if 
they were actually distinct plants. Such, as he says, is the only 
logical or intelligent method of treating them with any hope of 
recognition. Of course such a system does not, or for a while 
