1438 



PLANT BREEDING 



ii) Achenes large. 



12) Achenes of t\pe Zelenka 



13) Achenes not spotted. 



14) Flowering rather late. 



15) Badly attacked by rust. 



Achenes small. 



Achenes of type C.ajdukox'ikij (2). 



Achenes spotted. 



Flowering very late. 



Not attacked bv rust. 



The individuals of the first generation were not luiifo/ni and showed 

 several degrees of intermediate types which was to be anticipated, seeing 

 that the mother plant was heterozj^gous. Nevertheless , it was the 

 character of the male plant which predominated, especially in the strncture 

 of the leaves, and in the branching. As for the resistance to rtist, it turned 

 out that all the plants with green leaves, that is to say those which 

 resembled the mother plant, were very strongly attacked by the pa- 

 rasite. The rust also attacked a sm.all part of the plants with grey-green 

 leaves, i. e. those intermediate in structure between the female and 

 male parents. All the other plants, with silver5"-grey leaves resembling 

 those of the male parent, were not subject to rust. The fact that 2-3 of 

 the individuals were resistant to rust showed that the investigator was on 

 a good track, and although among these individuals there was not one 

 that was interesting from the agricultural point of view the researches 

 were followed up in I915. 



For the second generation the observations were made in 307 indivi- 

 duals reproduced from the seeds of plants which had not been attacked 

 by rust. In this generation a considerable number of types were obtained 

 in which were combined, in various proportions , the characters of one or 

 the other ancestor. Though it was not possible to find any individital 

 presenting a pure reproduction of the characters of its forebears, yet types 

 were often observed that were ver}- close to one of the ancestors and only 

 differed from it in one or two characters. At the same time a considerable 

 mmiber of individuals were observed which occupied an intermediate po- 

 sition between the two original parents, as had alread}^ been noticed among 

 the individuals of the first generation. Neglecting other characters of the 

 h\-brids of the second generation, their behaviour with regard to rust may be 

 indicated. It must be remembered that the year 1915 was most excep- 

 tional for the spread of this disease. The heavy summer rains encourag- 

 ed the de\'^lopment of the parasite so that by mid-August nearly all the 

 leaves of the vSunflower were withered in a very large number of plants. But 

 observations made in this year, so favourable to rust, showed that V4 of 

 the hybrids resisted the disease. The distribution, with reference to their 

 structure, of the leaves which were attacked by rust and those which were 

 resistant to it, was as follows : 



(2) The achenes of the sunflower Zelenka are chfiracterised by the presence of a cuirassed 

 layer and by their striped coats, while in those ol the sunflower C.ajdukovskii there is also a 

 special pigment soluble in water which is localised in the corky layer. See Bulletin ot Applied 

 Botany, No. 4-5 (79) PP. 574-576. Petrograd, 1915. 



