386 BROOKLYN BOTANIC GARDEN MEMOIRS 



B. racemosus. These results correspond exactly with the infecting 

 capacity of conidia from the same hosts. 



The evidence is quite conclusive for the existence of highly special- 

 ized races in the grass mildew. For the most part these races are 

 definitely restricted to the species of a single genus of host plants. 



Erysiphe Galeopsidis DC. Neger (107) tested the infecting 

 capacity of the mildew on Galeopsis tetrahit and found that this host 

 was infected, while negative results were obtained on Calaniintha 

 acinos, Glechoma hederacea and Stachys recta. Salmon (128) obtained 

 positive results with the mildew from Ballota nigra on this same host 

 but failed to infect Salvia verticillata and Leonurus cardiaca. 



Erysiphe Polygoni DC. Neger (107) used the mildew from the 

 following hosts : Galium silvaticum, Heracleum spondyliiim, Hypericum 

 perforatum, Ranunculus repens and Trifolium incarnatum. Positive 

 results were obtained when the mildew was sown on plants of the same 

 host from which it was obtained and negative results on all other hosts 

 tested. In one case he noted a slight infection of Galium silvaticum 

 with conidia from Ranunculus repens but this was probably a foreign 

 infection. 



Salmon (123) successfully infected Pisum arvense with conidia from 

 P. sativum. Other legumes gave negative results. Conidia from 

 Trifolium pratense infected this host but gave negative results on 

 seven other species of this genus as well as on species of other genera 

 tested. 



Microsphaera Astragali (DC.) Trev. The only results recorded 

 for species of this genus are those of Neger (107). He infected Astra- 

 galus glycyphyllus and A. cicer with conidia from the former. Three 

 other hosts gave negative results. 



Uncinula aceris (DC.) Sacc. and U. salicis (DC.) Winter. Neger 

 (107) used conidia of the former species from Acer pseudoplatqnus to 

 successfully infect A. pseudoplatanus and A. campestre. Conidia of 

 the second species from Salix purpurea infected 5'. purpurea and S. 

 caprea. 



Phyllactinia corylea (Pers.) Karst. Neger (107) reports one test 

 with conidia from Corylus avellana, these failing to infect the same 

 host. Voglino (166), using conidia from Corylus, infected Corylus 

 but not Carpinus, and conidia from Carpinus infected Carpinus but 

 not Corylus. He further found that ascospores from Carpinus infected 

 Carpinus but not Fagus, while ascospores from Fagus infected Fagus 

 l)ut not Carpinus. 



Sphaerotheca Hamuli (DC.) Burr. Salmon (128) used conidia of 

 this mildew from Potentilla reptans to infect P. reptans; no infection 

 occurred on Agrimonia Eupatoria, Alchemilla arvensis, A. vulgaris, 

 Fragaria (cult, sp.) Poterium officinale nor Spiraea ulmaria. 



