698 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



are also fewer ? If so, it seems strange that B. tectorum should also have 

 proved immune, because its stomata are more numerous than those of 

 B. madritensis, and hardly smaller than those of B. sterilis. And the 

 results are similar with other factors. . . . We are hence driven to con- 

 clude that the factors which govern predisposition on the one hand and im- 

 munity on the other are similar to those which govern fertility and sterility 

 of stigmas to pollen, and I have elsewhere * shown that parallels between 

 the behaviour of pollen (which is, after all, a kind of spore) towards the 

 stigma of the receptive plant in cross-breeding and of these uredospores 

 tow ards their host-plants multiply as we examine them. The importance 

 of all this is, I think, that it justifies the hopes of those who believe that 

 the constitution of plants can be so modified by breeding and selection 

 that disease -resisting varieties should be no more difficult to evolve than 

 varieties which refuse to cross with certain other forms. Only we must 

 not forget that the fungus is also capahle of being bred or selected, and 

 prepotent varieties of spores are just as much realities as prepotent pollen." 



R.I.L. 



Hybridisation. 



Hybrids, Preliminary Account of Variation in Bean. By R. A. 



Emerson (U.S.A. Exp. Stn., Nebraska). — The author here deals only 

 with racial hybrids of Kidney Beans. The characters chosen were yellow, 

 green, and blue-green pods ; stringy and stringless pods ; long and short 

 pods ; round and flat pods ; white, red, brown, black, and variously 

 mottled seeds ; oblong and nearly round seeds, &c. 



After describing the precautions taken, and methods of artificial 

 pollination, the author proceeds : — " When ripe, the hybridised seed is 

 gathered and compared with self- fertilised seed from the two parents to 

 determine whether any tendency toward xenia exists." 



The seeds are sown in the garden and protected against crossing by 

 wire netting. 



All racial hybrids of beans yet produced by the author showed little 

 variation in the first generation, but pronounced variation in the second 

 and third generations. Three photo-plates illustrate many instances 

 of such variations. 



With regard to the " common characters," i.e. of both parents, such 

 are usually reproduced in the hybrids with little variation. 



When both parents have yellow or green pods, such are reproduced ; so 

 also with other features, as stringy pods, dwarf habit, &C. 



" Differentiating characters ' usually unite and form " intermediate 

 characters." 



Blending of colours occurs, as when a blue-podded variety is crossed 

 with a white one : the result is brown. The white seeds of ' Navy ' unite 

 with the black seeds of ' Challenge Black ' to form spotted seeds, the light 

 spots being grey. 



Similarly intermediate results followed between stringy and stringless 

 pods, and Beans of different shapes. 



" Mosaics " occur when the two colours remain distinct. Then a 



* J 'roc. Cambridge Phil. Soc. vol. xi. pp. 320-328. 



