EUSTS. 103 



of mint, especially tiie watermint_, about the month 

 of August. We have found a few of the two-celled 

 spores of the Puccinia imbedded in the pustules of 

 this rust almost constantly, whilst the one-celled 

 spores are not uncommon in the pustules of what 

 is regarded as the true mint brand {Puccinia Men- 

 thee., P.). 



In spring the young leaves of the periwinkle 

 {Vinca major) will, in some situations, become 

 thickened considerably, and ultimately browned on 

 both faces with the pustules of a rust (Trichohasis 

 Vincce), which though covered with a conidioid dust 

 are often very tardy in bursting the epidermis. It 

 is almost impossible, after the pustule is ruptured, 

 to find one in which the bilocular spores of Puccinia 

 (fig. 132) are not largely intermingled with the 

 unilocular spores of the ^^rust'^ (plate YI. fig. 131). 

 Later in the season by two or three months, other 

 leaves of the same plants will be found occupied 

 by the smaller and more widely scattered pustules 

 of Puccinia Vincce, in which the unilocular spores of 

 the ^^rust ^' will seldom be found. In this instance 

 the leaves are scarcely thickened, and the colour of 

 the spores is much darker. The under surface of 

 the leaves is commonly alone occupied, and corre- 

 sponding paler spots on the upper surface indicate 

 the presence of the parasite beneath. 



The garden and field bean is Hable in some sea- 

 sons to become quite rust-coloured in consequence 

 of the profusion of spores with which the leaves 



