[ 8oo ] 



satisfactorily established as yet and it may be looked upon 

 in the light of a theory for the present. 



I >37 1 - Jacob Eriksson, a Swedish botanist, who has 

 recently made a very minute study of rust, has discovered 

 that the black or dark-brown rust (teleuto spores) of wheat 

 retains its germinating power for two winters. This is a 

 discovery of great practical usefulness, as the lesson to be 

 derived from it is that the cultivation of wheat should be 

 suspended in a particular locality for two years after there is 

 a severe attack of rust. The utility of such suspension will 

 be further apparent from another of Eriksson's discoveries, 

 viz. } the spores of rust travel only 10 to 25 metres from the 

 source of infection. So if a field shows rust very badly one 

 year there is no reason why a field 30 or 40 yards away from 

 it should not be cultivated with wheat the next year. Eriksson 

 has made another important discovery with regard to rust, 

 that is, the infection may come either from uredospores, or 

 teleutospores, or aecidiospores, or from a corpuscular germ of 

 the fungus discovered by Eriksson in the seed itself. The 

 microscopic appearance of these corpuscles is oblong, slightly 

 recurved and occurring either singly or united. These germs 

 give rise to intercellular mycelial development. 



1,372. Humidity and heat are alone required for germina- 

 tion of uredo and aecidiospores. Teleutospores require a 

 period of repose before it is active. In pickling wheat seed 

 before sowing one kills only the teleutospores. The other 

 sources of infection are not done away with. So even after 

 sowing pickled wheat seed one may have rust in wheat, 

 the infection coming from the aecidia or cluster cups on 

 some other plant, or uredospores blown along by the wind 

 from other wheat plants, or from germinal corpuscles inside 

 the seed. The aecidial stage, at least in the case of Indian 

 wheat rust, not being definitely established, only the uredo 

 and teleuto-stages are represented in the annexed figure 

 (Fig. 75)- 



