20 Colour and other Characters in the Potato 



towards greater length and approaching the pebble shape. In diagram 

 the type and extreme variation may be represented as below : — 



Fig. 1. These drawings are tracings of sagittal sections of potatoes — the long and trans- 

 verse axes are shown — the depth cannot be shown. 



Height and breadth are here represented, the depth being relatively 

 great. 



The " round " type is not a potato that recommends itself for its 

 beauty or its economic qualities as regards shape ; its merit is derived 

 from the fact that there is very good reason to regard it as a gameti- 

 cally pure type, and that " roundness " in the sense in which it has 

 been used here is a simple Mendelian character. The further evidence 

 in support of this thesis will appear as we proceed to discuss other 

 shapes. 



A seedling of " Flourball " was selfed in 190G, and in 1907 a large 

 number of seedlings were raised from it, one only of which was again 

 selfed in 1907. The plant was carried forward by tubers to 1908, 1909 

 and 1910. In both 1907 and 1908 it produced seed, but in these two 

 years only four plants came to maturity, and they produced the tubers 

 numbered in Plate VII, D\ D\ 1908, D^ and D\ 1909. The seedlings 

 from 1909 seed have not yet formed their tubers. 



The tubers of plant D are quite unlike the "rounds" of the A 

 family, they are oval and more or less kidney-shaped. The offspring 

 of these, only four in number (excluding the seedlings now growing), 

 comprise distinct types. 



