R. N. Salaman 29 



K'^ is an example of a pure "deep "-eyed potato; all the 284 

 seedlings of which are " deep "-eyed. 



This family, K^, further illustrates a curious phenomenon. Certain 

 individuals, such as K^^-\ Nos. 28, 84 and 95, appear at first sight to be 

 " shallow "-eyed. When, however, they are examined with their sister 

 tubers from the same plant, it will be seen that the "shallowness" is 

 only present at those points where an outgrowth or protuberation is 

 taking place : elsewhere in the same tuber or on its sisters, the eyes are 

 "deep" K^'-^K No. 28 is apparently "shallow," but here also outgrowths 

 are just beginning. A true " shallow "-eyed potato is "shallow" in 

 every tuber of the plant and a true " deep " is equally " deep " in every 

 tuber. The heterozygote is more variable and, though " deepness " is 

 dominant, the eye is often shallower than in the tubers of a pure 

 dominant "deep" eye. 



The potato " eye " is therefore, like shape, a distinct character 

 inherited on Mendelian lines. 



The Colour of Tubers. 



The colour is due to the presence of pigmented cell sap in the 

 cells of the superficial layers. The white skinned or, more correctly, 

 yellow skinned tuber, owes its colour on the one hand to the presence 

 of the cork in the upper layer of the corky tissue, and on the other 

 to the absence of any red or purple pigment. The red potato contains 

 a vermilion pigment in solution and the black potato, which is in 

 reality an intense purple, derives its colour from a deep blue purple 

 sap pigment which, seen under the microscope in contrast with the 

 red, is quite distinct. 



It was pointed out in the Introduction that potatoes of all colours, 

 including the whitest — with white flowers — showed more or less purple 

 pigment in the shoots, arising from the tubers in spring, if not in the 

 haulm also. Vilmorin do), in his catalogue of all the known varieties, 

 makes three classes in which the tubers possess white shoots ; it is 

 probable that small deposits of pigment were overlooked. Out of the 

 1200 separate and distinct varieties he describes some 45 as having 

 white shoots. Often the pigment occurs in punctate deposits which 

 need a lens to distinguish them clearly, but the pigment is unmis- 

 takably present. From this fact it would seem clear that all tubers, 

 coloured or not, possess the chromogen base, i.e. using the notation 



