RUSTS. 103 



of mint^ especially tlie watermint^ about tlie 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) wiW, in some situations^ become 

 thickened considerably^ and ultimately browned on 

 both faces with the pustules of a rust {TricJwhasis 

 • 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 VI. 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 liable in some sea- 

 sons to become quite rust-coloured in consequence 

 of the profusion of spores with which the leaves 



