N. I. Vavilov 61 



immune species as Tr. vulgare. Tr. durum and others (except Tr. 

 monococcum) are descended. This view, as is known, has been con- 

 firmed in our days by the finding of numerous forms of wild Tr. 

 dicoccoides in Palestine and Syria by A. Aaronsohn, and in Persia by 

 Strauss. In accordance with this view we find in the species Tr. 

 dicoccum, races both immune and susceptible to mildew and brown rust. 

 The susceptibility to brown wheat rust and mildew of some races of 

 wild Tr. dicoccoides, which were kindly sent to me by Mr A. Aaronsohn 

 and were examined in Moscow in their relation to fungi, once more con- 

 firmed their near relationship to cultivated wheats. Prof Tschermak 

 and A. Aaronsohn proved also that Tr. dicoccoides gives fertile hybrids 

 with cultivated wheats (14). 



Funded Reactions of Species of Oats and their Genetic 

 Relationships. 



The same parallelism of fungal reacti(jns and the genetic relations 

 of plants is observable in oats. According to the present views which 

 are based on systematic study and experiments in the crossing of wild 

 with cultivated forms, oats have a polyphyletic origin. According to 

 recent work by Dr Trabut in Algeria (13), Dr Thellung in Switzerland 

 (12) and A. F. Malzev in Russia, we regard A. fatua L., A. sterilis L. 

 and A. Ludoviciana Dur. as the ancestors of our cultivated forms 

 A. sativa L. (A. diffusa Asch. and Gr., and A. orientalis Schreb.)^ 



As was said before, the representatives of all these species examined 

 in Moscow proved to be equally susceptible to the narrowly specialized 

 crown rust P. coronifera, like the majority of cultivated oats. 



A. strigosa Schreb. and A. hrevis Roth., two rarely cultivated species, 

 which are morphologically much alike, and which by our crossing in 

 Moscow proved to give fertile hybrids^ are relatively immune to crown 

 rust. In this respect, they are distinguished from the above-mentioned 

 wild and cultivated oats. 



Many attempts at crossing of A. strigosa (two varieties) with culti- 

 vated A. sativa (A. diffusa Asch. and Gr.) repeated during two years in 

 the Moscow Agricultural Institute proved to be unsuccessful, whereas 

 under the same conditions the crossing of A. fatua. and A. sativa. was 



1 The origin of naked cultivated oats, represented by very different morphological 

 forms hitherto, is far from being clear. 



2 This crossing was done after their similar reaction on fungi was known to us, and 

 in this case the similarity in fungal reaction suggested the possibility of crossing these 

 two species. 



