B. 1'. I.— 102. V. I'. 1'. 1,-117 



INVESTIGATIONS OF RUSTS. 



ADDITIONS TO OUR KNOWLEDGE OF LIFE HISTORIES. 



In many iii.stancos, without any oxpoiinicntal i)roof, it i.s inferred 

 that there is a connection between the diil'erent forms of rust occur- 

 ring on the same host plant simply because of their constant associa- 

 tion with each other. Sometimes it is afterwards demonstrated that 

 these inferences are wrong-, though they are probabh' correct in a 

 majority of cases. Studies of the following species were made with 

 the view of obtaining a more accurate knowledge of their life liistory. 



PjUphorbia Rust {Uronu/ces enphorhlce, C. and P.). 



Until the experiments herein described were performed it iiad not 

 been demonstrated that there is any connection ])etween the an-idial 

 and other stages of this species, although experience naturally leads 

 one to think that there is. They are in very close association on the 

 same plant, the jvcidium appearing tirst, quickl\' followed by the 

 uredospores. In the spring of 1893 Mr. ,1. B. S. Norton, now pro- 

 fessor of botany at the Maryland Agricultural College, while engaged 

 in experiments in the germination of weeds in the greenhouses of the 

 Agricultural Experiment Station at Manhattan, Kans., called the 

 writer's attention to a ver}^ 3'om^S' I'usted seedling of Eu.j>horhia di^ntata. 

 \\\ this instance, as is usually the case with the young plants of this 

 host, the pods were first badly afl'ected by fecidia. This fact, taken 

 together with the common observation that the seed pods of this host 

 are usually affected by all stages of the rust, led at once to the thought 

 that it was a case of rust propagation through the medium of the germi- 

 nating seed of the host, something not before demonstrated for any 

 other species in the entire group of Uredinese, so far as the writer 

 knows, unless we except the single instance of the experiments of 

 Doctor Eriksson" with Puccinia glumarum? The seed used by Mr. 



« Vie latente et plasmatique de certaines Uredinees. Compt. Rend., 1897, pp. 

 475-477. 



^ T. S. Ralph, in Victorian Naturalist, Vol. VII, p. 18, de.scribes an instance of a 

 rust attacking the seed of Senecio vulgaris, stating that "with the microscope we are 

 able to trace the fine yellow sporular matter into the covering of the seed, and into 

 the seed itself;" but apparently it was not determine<l by further investigation 

 whether or not the rust was able to reproduce itself through the germinating seed. 



9 



