310 DISEASES OF CULTIVATED PLANTS 



soon become yellow and die, the disease gradually works 

 upwards. 



Uredospores subglobose, rough, 22-16 /x. 



Teleutospores mixed with uredospores in the same pustules, 

 elliptical, each cell being almost triangular, smooth, brown, 

 28-38x20-26^. 



Leptopuccinia. Teleutospores only known, germinating 

 on the living host. 



Hollyhock rust (Pucclnta malvacearum, Mont.) is a native 

 of Chili, and first occurred as a pest on the cultivated holly- 

 hock in Australia, soon afterwards entering Europe through 

 Spain, and at the present day is in evidence practically 

 wherever the hollyhock is grown. During the first period of 

 the disease, as is generally the case, it was practically 

 impossible to grow hollyhocks, but although yet present, the 

 fungus is not so exacting as it was, and rarely causes a serious 

 epidemic if ordinary precautions are taken. At the present 

 day the parasite has attacked most European wild plants 

 belonging to Malvaceae, the various mallows, etc., also certain 

 cultivated plants, Abutilon, etc. This fungus would be a 

 suitable subject for determining whether biologic forms are 

 evolved within a comparatively short period of time. The 

 fungus was first recorded in England in 1873, and it would 

 be interesting to ascertain whether the fungus attacking 

 mallows can infect hollyhocks, and the reverse. 



The teleutospore stage is the only one formed, and the 

 spores germinate in situ, producing secondary spores which at 

 once infect other leaves or plants, thus spreading the disease 

 after the manner of uredospores in allied species. It has 

 been stated that the teleutospores formed in the autumn act 

 as resting-spores, not germinating until the following season. 



Sori forming small, prominent, hard, brown pustules, 

 usually present in considerable numbers on the leaves, some- 

 times also on the stem, calyx, and fruit. Teleutospores 

 ovoid-oblong, brownish, smooth, slightly constricted at the 

 septum, obtuse or narrowed at the apex, 35-75 X 12-16 /x, 

 pedicel very long. 



I have proved by repeated experiments that if plants of the 

 first year are attacked, they remain free from the disease in 

 spite of attempted infection. On the other hand, if seedlings 

 escape the disease the first year, they are very susceptible the 

 second year. This suggests similia similibus curantur, or, 



