Parasitic Fungi of Illinois. 423 



It is unfortunately necessary to discard this last well-known 

 name in favor of the one previously given by De Candolle to 

 one of the many forms of the species. This is to be regretted 

 the more as the name, aim,, taken from only one among so 

 many hosts, fails to express any true characteristic of the spe- 

 cies as now understood. Some writers whose opinions carry 

 great weight in all matters concerning fungi, would consider 

 this sufficient ground for disregarding the law of priority, and 

 would select from the names that had been given to the species, 

 the one that seemed to them to be most appropriate, even going 

 so far as to give a plant an entirely new name, because 

 found to occur on other hosts than the one from which its name 

 was derived. The case of Plujtophthora omnivora^ De Bary, may 

 be taken to illustrate this usage. Hartig described a parasite oc- 

 curring on young birch seedlings as Peronospora fagi (Zeitschr. 

 f. Forst- und Jagdwesen., VIII. (1875), p. 121). Schenk de- 

 scribed a similar parasite on Sempervivum as Peronospora semper- 

 vivi (Sitzungsber. d. Naturf. Gesellschaft zu Leipzig, July, 

 1875). De Bary (Morph. und Phys. der Pilze, IV., pp. 22-27) 

 finds these two species to be identical, and that the same thing 

 also occurs on Clarkia. He, therefore, in transferring them to 

 his new genus, Phytophthora, writes P. omnivora, entirely disre- 

 garding both of the previously given names, although, in this 

 case, there could be no question of the identity of the forms 

 first described, but only of the appropriateness of the older 

 names in the light of the increased knowledge of the species. 



While it is doubtless very desirable to have species appro- 

 priately named, it is easy to see that this practice, if usually 

 followed, would lead to endless confusion; for each addition to 

 our knowledge of a species would necessitate, or at least permit, 

 a change of name. Here, as in other branches of biology, the 

 only safe rule seems to be to adhere rigidly to the law of pri- 

 ority whenever the older name is at all admissible. If this 

 species never occurred on Alnus the retention of the name M. 

 alni would be much more questionable. 



This species is not reported as occurring on Sijringa, in 

 Europe, although abundant there on other hosts. This seems 

 singular when it is remembered how frequently our lilacs are 

 attacked by it, and naturally leads to the question whether, 



