September 30, 1898.] 



SCIENCE. 



431 



aecidium on Paris ia 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 in- 

 troduced 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 Phalaris 

 seem to agree in speaking of P. sessilis, P. 

 Digraphidis and P. Phalaridis as distinct 

 species, although Plowright considered P. 

 Paridis to be distinct from P. Digraphidis, 

 whereas Magnus considered the two to be 

 what he calls adaptive races (Gewohnheits- 

 racen) of the same species. Magnus speaks 

 of the three species as biological species, 

 which he distinguishes from adaptive races, 

 the latter including forms in which, although 

 the secidium may be produced on different 

 hosts, it does not appear to be so frequent 

 or so well developed on some hosts as on 

 others, showing in the one case that the 

 adaptation is more complete than in the 

 other. Klebahn, although admitting that it 

 is not of real importance whether one re- 

 gards such forms as the Puccinise on Phalaris 

 as species or races, nevertheless states that 

 he sees no reason why they should not be 

 considered to be genuine species rather than 

 races. 



Another instance in point is the group of 

 secidia generally known as species of Peri- 

 dermium, which infest species of Pinus. 

 It had for some years been recognized that 

 the secidial stage of the cortioolous form 

 of Peridermium Pini was not the same as 

 that of the form on the leaves, but in re- 

 cent years the subdivision has been carried 

 much farther, owing to cultures made by 

 Klebahn, Edouard Fischer, Kostrup and 

 others. The former has distinguished at 

 least seven species of Peridermium on Pinus 

 sylvestris alone, whose uredo and teleuto- 

 spores are to be found in the species of 



Coleosporinm which grow upon different 

 genera of Compositte, Scrophulariacese and 

 CampanulaceEB. Although Klebahn is in- 

 clined to see minor differences in the shape 

 and markings of the Eecidial spores of some 

 of the species, it must be admitted that the 

 differences in some cases are so slight, both 

 in the case of the secidial spores and the 

 corresponding teleutospores, that were it 

 not that cultures show the connection be- 

 tween the form of one host with that on 

 another to the exclusion of other hosts it 

 is hardly likely that many botanists would 

 consider them as distinct species. 



The most suggestive Uredinaceaj for our 

 present purpose are the different species of 

 Puccinia which attack grains and other 

 grasses, for a knowledge of which we are 

 indebted to the researches of Eriksson and 

 Henning in Sweden, whose work is cer- 

 tainly a model of careful investigation. I 

 take it for granted that most of my hearers 

 are already acquainted with the character 

 of the work in question, and we need stop 

 to consider only those points which bear 

 upon the subjects we are discussing. Of 

 the three common rusts which affect grains, 

 Puccinia graminis, P. rubigo vera and P. coro- 

 nata, the aecidia are to be found respectively 

 in Aecidium Berberidis, Aec. Asperijolii and 

 Aec. Rhamni, according to the previously 

 accepted view in regard to those species. 

 Judging by the morphological characters of 

 the teleutospores and the uredospores alone, 

 these three species occur on a larger num- 

 ber of different grasses. In making inocu- 

 lations to ascertain the facts in regard to 

 the secidia of the species, Eriksson and 

 Henning found that what was supposed to 

 be P. graminis growing on Phleum pratense 

 and Festuca elatior had no secidia, and they 

 described this form under the name of P. 

 Phlei-pratensis. Puccinia coronata is sepa- 

 rated into two species, P. coronifera and P. 

 coronata, the former having its secidium on 

 Rhamnus catharticus, the latter with secidia 



