388 BROOKLYN BOTANIC GARDEN MEMOIRS 



twenty-one species which belong to genera of this subgroup, but was 

 able to infect only four species of the genus Taraxacum: T. officinale, 

 T. ceratophorum, T. palustre and T. erythrospermum. Three other 

 species of this genus tested remained free from the fungus. In many 

 of his experiments, Liidi kept control plants of T. officinale and these 

 were readily infected by the swarmspores. 



Albugo Candida (Pers.) Roussel. Eberhardt (31, 32) has made 

 inoculation tests with this parasite. His results are as follows: 



1. Conidia from CapseUa Bursa-pastoris infected C. Bursa-pastoris, 



Arabis alpina, Iheris amara and Lepidium sativum. 



2. Conidia from CapseUa Heegeri infected C. Bursa-pastoris and 



Lepidium sativum. 



3. Conidia and oospores from Lepidium sativum infected L. sativum 



and CapseUa Bursa-pastoris. 



4. Conidia from Arabis alpina infected A. alpina, A. Halleri, A. 



hirsuta, A. turrita, CapseUa Bursa-pastoris, Cardamine pratensis, 

 Iberis amara, Lepidium sativum, Senebiera coronopus, but not 

 Brassica napus, B. nigra, B. oleracea, Raphanus sativus nor 

 Sinapis arvensis. 



5. Conidia from Brassica Rapa infected B. Rapa, B. nigra, B. oleracea 



(var. botrytis, capitata, congyloides) , Diplotaxis tenuifolia and 

 Sinapis arvensis, but not CapseUa Bursa-pastoris, Iberis amara 

 nor Lepidium sativum. On the basis of these experiments, 

 Eberhardt concludes that there are two specialized races of 

 the parasite: 



1. On Arabis-Capsella-Lepidium. 



2. On Brassica-Diplotaxis-Sinapis . 



Melhus (99) has also tested the infecting capacity of Albugo Candida 

 on the radish {Raphanus sativus). He was able to infect this host, 

 twenty-two varieties being equally susceptible, also Raphanus caudatus, 

 Brassica alba (white mustard) and Brassica oleracea (cabbage, fifteen 

 varieties). In the case of the latter plants infection was less certain 

 than for the radish. The following plants gave negative results: 

 Brassica rapa (turnip, ten varieties), B. nigra (black mustard), B. 

 campestris (rutabaga, three varieties), CapseUa Bursa-pastoris (shep- 

 herd's purse), Lepidium sativum (garden cress), L. virginiciim (wild 

 pepper grass). Sisymbrium officinale, S. altissimum (hedge mustard), 

 Iheris umbellata (candytuft), Nasturtium officinale (water cress) and 

 Cheiranthus Cheiri (wall flower). 



Peronospora parasitica (Pers.) de Bary. Gaumann (59) has 

 carried out a few experiments with this fungus and finds a high degree 

 of host specialization. The fungus that occurs on CapseUa cannot 

 infect other Cruciferae. The same is true of the race on Brassica. 



