No. 381.] THE CONCEPTION OF SPECIES. 687 
As the subject is somewhat complicated, it will be well to 
consider a few prominent cases by way of illustration. An 
instructive case is that of the Puccinia on Phalaris arundinacea, 
referred to, among other subjects, by Magnus and Klebahn in 
papers published in 1894 and 1895. To the teleutospores was 
originally given the name Puccinia sessilis Schneider, which was 
found by Winter to bear its æcidia on A//ium ursinum. Later 
Plowright experimented with a species which grew on Phalaris 
whose teleutospores could not be distinguished from those of 
P. sessilis, but whose zecidia could be produced on Arum mac- 
ulatum, though not on Allium. To this physiological species 
Plowright gave the name of P. phalaridis. Still later Soppit 
discovered that a Puccinia indistinguishable from P. sessilis and 
P. phalaridis in its teleutospores produced its zcidia on Con- 
vallaria majalis. To this species he gave the name of P. 
digraphidis. Had these observations not been confirmed by 
others we might have doubted whether Winter, Plowright, and 
Soppit had not really experimented with the same species of 
Puccinia, but, owing to some accident of their cultures, had 
succeeded in inoculating only different hosts, whereas it might 
well be the case that the ecidia on the three hosts might by 
subsequent cultures prove to be the same ; and, in that case, 
P. sessilis would really be only an instance of a Puccinia which 
produces ecidia on three different hosts, not an infrequent 
case. The observations of Magnus showed that P. digraph- 
idis bore æcidia also on Polygonatum and Maianthemum, 
genera closely related to Convallaria. So far as concerned Poly- 
gonatum and Maianthemum, Soppit and Magnus'’s observations 
were confirmed by Klebahn. The case is complicated by a 
difference of opinion as to whether the æcidium on Paris is 
connected with P. digraphidis, or whether there is not a fourth 
distinct species, P, paridis, as believed by Plowright. 
We need not stop, to consider the further history of this 
complicated case, as it is introduced here merely to illustrate 
the method and tendency of recent workers in this field.! The 
above-named botanists, who studied the species of Puccinia on 
1 Those interested in the subject should consult Klebahn, “ Ueber den gegen- 
wartigen Stand der Biologie der Rostpilze,” in Botanische Zeitung, May 16, 1898. 
