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Proceedings of Indiana Academy of Science 



cies. In the case of Pnccinia triticina, uredinia appear in 6-10 days 

 after inoculation, development being most rapid in warm, sunny weather, 

 and slowest in cool, cloudy weather. In the case of leaf rusts of wheat, 

 rye, and barley the heavily infected leaves of seedlings die in about two 

 weeks after the uredinia appear, and the plants thus become free of the 

 rust unless I'einoculated. If the leaves have to support only a small 

 quantity of rust, infection may persist for some time, new uredinia being 

 produced toward the border of the mycelium until there are two or even 

 three concentric circles of uredinia around the uredinium first produced. 

 As these rusts usually are carried on seedlings upon which it is desirable 

 to produce as much infection as possible, it is necessary to transfer cul- 

 tures about once every three or four weeks. 



Fig. 3. Series of Wardian chambers for separation of rust cultures, showing right- 

 hand two with sash down as used with spray and left-hand two with sash up and 

 curtained off with muslin. 



In the case of the rust of snapdragon, Pnccinia Antirrhini, where 

 the infected stems may not die for some time, the rust may continue 

 to sporulate for two or three months, until the infected parts are killed. 

 Corn rust, Pnccinia Sorghi, maintains itself in the greenhouse as the 

 funnel of unrolling young leaves makes an ideal moist chamber for 

 spore germination. Whenever plants or plant parts overlap so that 

 water persists on the lower leaves and a high humidity exists, the rusts 

 will continue to reinoculate, provided temperatures are favorable for 

 spore germination. Where comparative studies of different cultures are 

 being made it usually is more desirable to limit the inoculation only to 

 certain plants and therefore by proper spacing and care in watering, 

 the rusts are prevented from reinoculating. 



9. Comparative Study of Cultures. Where more than one cultm'e 

 of the same species of rust are being studied in order to determine if 

 specialized races or strains exist and their behavior upon different spe- 



