(4) 
CHAPTER XIII. 
{ 
| 
THE ARTIFICIAL INFECTION OF PLANTS. 
IN order to ensure success in the artificial infection oi 
plants, attention to several little details is absolutely neces- 
sary. Of course, if you simply wish to produce 4ccdium 
urtice on a cluster of nettles, you may throw a handful o/ 
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 Aécidium 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 zcidia 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 ofter 
happens that more than one species attacks the same host- 
plant; P. magnusiana, trailii, and phragmitis, on the reed 
for instance. 
The first thing to be done is to provide suitable plant: 
for infection. These should, it is hardly necessary to state 
be healthy, and have had time to become established before 
