A LECTURE ON THE HEREDITARY CHARACTERS IN THE POTATO. 37 



the more close up the parents are, the greater the proportion of close up 

 offspring, and in one case I have been able to obtain plants which 

 breed pure to the close up condition. This close up condition of the 

 tubers is economically of great importance, and one which is not always 

 to be found in our domestic varieties. That the tubers should cluster 

 closely round the stem is of value, not only in the digging, but because 

 it allows the greatest use to be made of the land. Careful analysis of 

 the cropping of over 1300 individuals shows that of all the good 

 cropping seedlings 60 per cent, were close up plants, and 20 per cent, 

 more or less long stolon plants. In some individual families the 

 correlation between the position of the tuber on the stolon and the 

 formation of a good crop was considerably closer than this. 



Cropping. — The crop of tubers which a plant bears depends on a 

 number of circumstances — on the soil, on the season, on the time of 

 planting, and other causes ; but in respect to the cropping of seedlings, 

 treated as far as may be in an identical manner, in addition to these 

 external factors there are others. As has already been shown, there is 

 a very distinct relationship between the close up disposition of tubers, 

 which is probably controlled by one or more pairs of factors, and the 

 size of the crop ; and, further, it was found last year, when the great 

 drought affected adversely all the potato plants, that the prone indi- 

 viduals, on the whole, bore better crops, and a far greater percentage 

 of them were good croppers than the uprights. The hushy or hybrid 

 plants had, though a smaller percentage of good croppers amongst them 

 than the prones, still a higher percentage than the uprights, who fared 

 the worse for lack of moisture. It may be that besides this there is 

 some factor definitely controlling the cropping, and I am inclined to 

 think that it is very likely that there is such a factor. It is improbable, 

 however, that one will be able to get at closer quarters with such, if 

 indeed it exists at all. 



My observations show that one has control of two vitally important 

 factors in respect to cropping; the one is the disposition of the tubers 

 and stolon length, and the other the habit of the haulm. 



The Tuber. — Of the tuber characters only those in respect to shape, 

 eye, and colour have been analytically worked out. 



Shape. — The shape of tubers has long been a puzzle to growers. 

 A variety of shapes are described by such terms as cylindrical, 

 kidney, oval, pebble, round, and the like, but it is only an analysis on 

 Mendelian lines which is able to bring any order out of this apparent 

 confusion. The fact is that there is, on the one hand, a clearly defined 

 pair of characters controlling length of tuber, and, on the other, a 

 fluctuating variation not only affecting the families as a whole, but also 

 the tubers of each individual plant. At an early stage of the work it 

 became clear that there was one form of potato tuber which when 

 selfed bred true, and which when crossed was recessive. This is the 

 round potato, i.e. a potato tuber with a shortened axis, its vertical 

 diameter being equal to, or often less than, its tranverse. Such a 

 round tuber, with its depression at the point of insertion of the stolon, 



