( IH ) 



CHAPTER XIII. 



THE ARTIFICIAL INFECTION OF PLANTS. 



In order to ensure success in the artificial infection of 

 plants, attention to several little details is absolutely neces- 

 sary. Of course, if you simply wish to produce ^cidmm 

 tirticm on a cluster of nettles, you may throw a handful of 

 Carex hirta affected with Puccinia upon the ground where 

 the nettles grow in autumn, and, trusting to chance, you 

 will probably find them bearing the yEcidium the following 

 spring. But such a procedure is open to many objections ; 

 the wind may blow away your Carex during the long 

 winter and spring months either before the Puccinia has 

 germinated or before the nettles have appeared above 

 ground. A still greater objection is, that even if a few 

 clusters of aecidia happen to be produced on the nettles, 

 you have no proof that they arose from the Puccinia you 

 threw down. Still more important is it to avoid this clumsy 

 method of "laying on," if you are investigating the life- 

 history of any particular species of Uredine, for it often 

 happens that more than one species attacks the same host- 

 plant ; P. inagmisiana, trailii, and phragmitis, on the reed, 

 for instance. 



The first thing to be done is to provide suitable plants 

 for infection. These should, it is hardly necessary to state, 

 be healthy, and have had time to become established before 



