1036 RESISTANT PI. ANTS 



never contract it. These differences might perhaps be still more clearly 

 shown if pure lines were used for experiment, which was not the case here. 



These experiments have also proved that among some descriptions 

 of one and the same variety of wheat, a certain agreement is found as re- 

 gards their resisting powers to smut, but that this is not observed in the 

 most important cultivated forms (ordinary and spelt). The experiments 

 made with common wheat and spelt generally showed that when a wheat 

 is resistant to smut, another belonging to the same botanical group does not 

 necessarily behave in the same way. The degree of predisposition must 

 rather be regarded as a character typical of the wheat under examination. 



The author also endeavoured, by infection tests, to study the influence 

 of external factors on the result of contamination with spores of the parasite. 

 Even in the case cf wheats which were regarded as prone to the disease the 

 figures obtained in the diiferent years for the same wheat differed greatly, 

 sometimes falling to zero. It follows that the fact that an artificially in- 

 fected wheat has not contracted the disease does not necessarily mean that 

 it is refractory to it. 



The great influence of external factors on the result ot infection partly 

 explains the contradictory observations made, especially by farmers, with 

 regard to the smut-resisting powers of different wheats. In well-conducted 

 experiments, however, a fair agreement of the different wheats is nevertheless 

 observed. For instance, out of 17 wheats studied by the author and after- 

 wards also tested by TubEuf and Hecke, the same wheats were found prone 

 or resistant to smut in all the investigations. The writer concludes that 

 Hecke's opinion that resistance to the disease is in each wheat a constant 

 character influenced by other factors is correct. 



Assuming that the degree of resistance is a constant character of the 

 wheat, it must be concluded that this character is hereditary. No such 

 experiments as were undertaken for " rust " have as yet been carried out, 

 to determine whether susceptibility to the disease is hereditary. The writer 

 does not think that the observations relating to rust can be extended 

 to smut. 



Without taking into account the question of heredit}', the attempt 

 has already been made to clear up the matter of the greater or lesser resistance 

 of certain wheats to smut. TubEiif suggested that a relation might exist 

 between resistance to smut and the rapidity of the germination of the wheat 

 grains, those wheats which germinate rapidly being the more resistant. 

 This opinion is also supported bj'- AppEL and Gassner, who claim to have 

 actually found such a relation. The writer's experiments nevertheless have 

 shown that these results do not admit of generalisation and that at any rate 

 this relation does not exist in a large number of common wheats, hard wheats, 

 winter and summer spelts. HeckE obtained the same residt. Nor is there 

 any relation between the germinating capacity and the smut resistance, as 

 was proved by the writer. 



The di ff erence in smut-resistance is thought b> the writer to be due 

 rather to differences in the chemical composition of the plantlets. The obser- 

 vations in respect to variou'=! diseases (rust, mildew, etc.), showing that the 



