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 Calamintha 
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 spondylium, 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 Piswm 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 pseudoplatanus to 
successfully infect A. pseudoplatanus and A. campestre. Conidia of 
the second species from Salix purpurea infected S. purpurea and S. 
capreda. 
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 
but not Carpinus. 
Sphaerotheca Humuli (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. 
