330 THE RUSTS OF NOVA SCOTIA. FllASEH. 



Olive (Annals of Botany, 22: 331-360. 1908) confirms the 

 work of Christman and Blackman and brings some of their 

 apparently conflicting results into harmony, but on the whole 

 confirming Christman's conclusion. 



In general the nuclear life history of a species showing 

 all the spore types is as follows : The mycelium which pro- 

 duces the pycnia and the aecia is uninucleate, as well as the 

 pycniospores. There is a fusion of cells in the aecia and the 

 aeciospores and the mycelium that produces the urediniospores. 

 and these spores themselves are bi-imcleate. Fusion of the 

 nuclei takes place in the teliospores, so that the basidiospores 



are uninucleate. 



. Spread of Busts. 



The question of how the rusts are spread and continued 

 from season to season is an important one in the case of the 

 grain rusts. Puccinia gramimis, P. Lolii and other destructive 

 grain rusts are heteroecious with hibernating teliospores, but as 

 has often been shown the aecial host is not sufficiently dis- 

 tributed to explain the regular and general appearance of these 

 rusts; in fact the general impression is that the barberry has 

 little to do with the spread of the grain rusts. -Where the 

 winter is not too severe probably the rusts are continued from 

 year to year by hibernating uredospores and mycelium. 

 Carleton (Bull. 16, Div. Phy. and Path. U. S. Dept. Agr., 

 1899) shows that several rusts winter over in the uredinial 

 stage. Bolley states definitely that in some cases the uredo- 

 spores may hibernate even in North Dakota and thus propagate 

 the rust. Investigation tends to show that uredospores may 

 winter and this favours the theory that spring infection comes 

 from this source. 



Another view is that the urediniospores are blown from 

 more southern localities, where the winters are mild, and prob- 

 ably this has much to do with severe outbreaks. The large 

 acreage of grains in all parts of the world and the known 

 fact that in dust storms particles of dust are carried long 



