NOTES ON SOME HYBEID TL^BEROUS SOLANUMS. 



127 



NOTES ON SOME HYBKID TUBEEOUS SOLANUMS. 

 By Eev. J. AiKMAN Baton, M.A., B.Sc. 



In order to get a clear start and to obtain reliable facts as to the unit- 

 characters of the potato and their inheritance, it seems at least desirable 

 to cross plants which are fairly typical members of pure lines of species 

 or varieties having distinct characters. None of the cultivated kinds 

 are of value for this purpose, all of them being already inbred hybrids, 

 as their selfed seedlings conclusively show. In the really wild types, 

 which reproduce themselves true from seed, being homozygotic, we 

 readily find material which answers the requirements. And it would 

 seem that, to ensure success and to check the accuracy of the result, 

 the selected individuals of the two wild types chosen for the experi- 

 ment should be carefully marked and continued for some years by 

 means of their tubers [as well as by selfed seed] in order (1) to 

 repeat the experiment with the same plants; (2) to make a com- 

 parison of the hybrids Fi with the parental types (both the hybrids and 

 parents being propagated by tubers, and the latter also by selfed seed) 

 during subsequent years; (3) to test whether Fa seedlings are more 

 vigorous than the corresponding parents, or differ from them in any 

 way with respect to given characters; (4) to observe whether selfing 

 the plants arising from tubers gives the same or different results 

 from those originally given by selfing the first-year seedlings. In each 

 year, every character which is similar, and every character which is 

 different in the case of the hybrids and the parent plants, with the 

 relative ratios, should be carefully noted, with photographs to scale, if 

 possible. This I am endeavouring to do. By the use of pure lines " 

 one is enabled, among other things, to eliminate, or at least to allow 

 for and discount, the element of fluctuating variability, which in the 

 potato is considerable. 



Among the pairs of types chosen in 1908 were the white-flowering 

 Solanum Commersonii and S. tuherosum (wild Mexican form). These 

 were crossed, S. tuberosum being the pollen-parent. A great many 

 of the resulting berries were seedless, this being a common result with 

 S. Commersonii. The number of berries having seeds obtained by the 

 cross was twelve, containing thirty-three seeds in all. [A number of 

 selfed berries containing fertile seed were also obtained at the 

 same time, but these do not at present enter into this result.] The 

 number of seeds in the berries varied from one to eight ; they were very 

 dark in colour, nearly black. The seed was sown on March 19, and 

 of the thirty-three seeds, which were plump and seemingly good, only 

 nine resulted in seedling plants. Two of these were kept in pots in 

 a greenhouse (except for about two months, July and August, when 



