520 MISCELLANEOUS BOTANICAL LETTERS. [1878. 



letter, of rearing a vast number of seedlings from cross-fer- 

 tilised parents, exposing them to infection, ruthlessly destroy- 

 ing all that suffer, saving those which resist best, and re- 

 peating the process in successive seminal generations. My 

 belief in the probability of good results from this process 

 rests on the fact of all characters whatever occasionally va- 

 rying. It is known, for instance, that certain species and 

 varieties of the vine resist phylloxera better than others. 

 Andrew Knight found in one variety or species of the ap- 

 ple which was not in the least attacked by coccus, and 

 another variety has been observed in South Australia. Cer- 

 tain varieties of the peach resist mildew, and several other 

 such cases could be given. Therefore there is no great 

 improbability in a new variety of potato arising which would 

 resist the fungus completely, or at least much better than 

 any existing variety. With respect to the cross-fertilisation 

 of two distinct seedling plants, it has been ascertained that 

 the offspring thus raised inherit much more vigorous con- 

 stitutions and generally are more prolific than seedlings 

 from self-fertilised parents. It is also probable that cross- 

 fertilisation would be especially valuable in the case of the 

 potato, as there is reason to believe that the flowers are 

 seldom crossed by our native insects ; and some varieties 

 are absolutely sterile unless fertilised with pollen from a dis- 

 tinct variety. There is some evidence that the good effects 

 from a cross are transmitted for several generations ; it 

 would not, therefore be necessary to cross-fertilise the seed- 

 lings in each generation, though this would be desirable, as 

 it is almost certain that a greater number of seeds would 

 thus be obtained. It should be remembered that a cross 

 between plants raised from the tubers of the same plant, 

 though growing on distinct roots, does no more good than 

 a cross between flowers on the same individual. Consid- 

 ering the whole subject, it appears to me that it would 

 be a national misfortune if the cross-fertilised seeds in 

 Mr. Torbitt's possession produced by parents which have 

 already shown some power of resisting the disease, are 



