7, =. 
v4 
OUR AMPHIBIOUS PERSICARIAS 247 
distinctions must be substituted that properly separate them, 
if we are to avoid the total confusion that has enveloped and still 
envelops the knowledge of these plants on the part, not only of 
our amateur plant students, but most botanists. 
7. Two different species of these plants may more or less 
resemble one another in one or other of their respective phases, 
and still be considered as distinct, provided they are sufficiently 
and specifically different in the other corresponding phase or 
phases; e. g. typical P. amphibia and P. emersa may look more 
of less alike in the aquatic, but are totally and unmistakably 
different in the terrestrial phases of each. 
8. The plants may be said to be normally aquatic or normally 
terrestrial or both, according as they bloom and fruit regularly 
and respectively in the aquatic, terrestrial or both phases together. 
g. Specimens of these plants are to be considered as in- 
complete, and therefore more or less useless for purposes of 
identification, that are not present in their several phases. A 
system of making herbarium specimens, or groups of several 
or many sheets under one number has been suggested. The various 
phases are to be lettered in addition to the sheet number. Thus 
840a is the aquatic typical, 84ok or any last letter used, the terres- 
trial, and the intermediate letters to represent the transition 
phases in order of resemblance to one or the other. 
10. Absence of any plant in America that perfectly cor- 
responds to the terrestrial phase of the typical European P. 
amphibia points to the fact that P. amphibia is not to be looked 
for on this side of the Atlantic, and that the name therefore should 
disappear from American manuals of botany. The absence, in 
Europe, as far as I can find of the Hartwrightianae as a group, 
i. e., plants with spreading herbaceous borders to the ochrea is 
worthy of note in emphasizing the above statement. 
11. Asystem of classification of the plants as Emersae, Hart- 
wrightianae, and the provisional Hydrophilae in the subgenus 
Potamocallis differs from previous treatment of the subject. 
12. Ecological study of these plants in the field can alone 
solve their relationships to one another, as also their eligibility 
to specific rank. Seasonal variations of respective phases must 
be watched with care and perseverance. 
Department of Botany, 
University of Notre Dame. 
