430 



SCIENCE. 



[N. S. Vol. VIII. No. 196. 



for supposing that, in the secidial stage, a 

 form of true sexuality occurs comparable 

 with what is known in some ascomycetous 

 fungi. Time alone will show whether this 

 present probability is a reality, but at any 

 rate the position of Uredinacese in regard 

 to sexuality is undoubtedly very different 

 from that of bacteria and Saccharomycetes. 

 One who takes up the recent descriptive 

 works on Uredinacefe is surprised to see the 

 number of species which depend on physio- 

 logical characters. The former method of 

 describing the species of this order from the 

 morphological characters of the teleuto- 

 sporic, the uredosporic and ajcidial stages 

 was certainly sufficiently perplexing, but 

 one almost gives up in despair on seeing 

 species in which the different stages are 

 identical in all respects, except that some 

 of them, usually the secidia, will grow only 

 on certain hosts. Facts like this are, of 

 course, only determined by artificial inocu- 

 lations, although they may sometimes be 

 suspected by the distribution of the different 

 stages in nature. In this complicated state 

 of things, more complicated than in any 

 other order of plants, we are compelled to 

 examine very critically the accounts of cul- 

 tures made even by botanists of high repu- 

 tation, and it is only natural that we should 

 hesitate to give implicit confidence to nega- 

 tive results unless the observations have 

 been repeated by other observers at other 

 times and places. Even from scattered 

 positive results one should avoid drawing 

 too wide general conclusions. We may 

 readily suppose that some of the supposed 

 distinctions in the choice of their hosts by 

 different UredinacesB will be proved here- 

 after not to be founded in fact, but, making 

 all proper allowances for possible errors in 

 observations and for hasty speculation in a 

 field where speculation is so easy and accu- 

 rate experiment so difficult, we have to 

 admit that in a good many cases surprising 

 results have been confirmed by repeated ob- 



servations and the tendency to split up spe- 

 cies on physiological grounds becomes more 

 and more marked. 



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 sub- 

 jects, by Magnus and Klebahn in papers- 

 published in 1894 and 1895. To the teleuto- 

 spores was originally given the name 

 Puccinia sessilis Schneider, which was found 

 by Winter to bear its secidia on Allium- 

 ursinwn. Later Plowright experimented 

 with a species which grew on Phalaris whose 

 teleutospores could not be distinguished 

 from those of P. sessilis, but whose secidia. 

 could be produced on Arum macidatiim though 

 not on Allium. To this physiological species 

 Plowright gave the name of P. Phalaridis. 

 Still later Soppit discovered that a Puccinia 

 undistinguishable from P. sessilis and P. 

 Phalaridis in its teleutospores produced its- 

 secidia on Convallaria majalis. To this spe- 

 cies 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 suceeeded in inoculating 

 only different hosts, whereas it might well 

 be the case that the secidia 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 Puc- 

 cinia which produces secidia on three differ- 

 ent hosts, not an infrequent case. The ob- 

 servations of Magnus showed that P. Digra- 

 phidis bore secidia also on Polj'gonatum and 

 Maianthemum, genera closely related to- 

 Convallaria. So far as concerned Polygo- 

 natum and Maianthemum, Soppit and. 

 Magnus's observations were confirmed by 

 Klebahn. The case is complicated by a^ 

 difference of opinion as to whether the 



