R. N. Salaman 9 



The colour of the stem is always correlated in some degree with 

 that of the tuber, but whereas one meets with innumerable white- 

 tubered plants, yet, as far as my experience goes, in all of these some 

 colour may be found, if not in the stem, then in the shoot which 

 emerges from the tuber in spring. 



Very definite Mendelian segregation of colour in the stem occurs 

 when the black or deep purple pigment, such as is seen in " Congo," is 

 introduced, but in the case of the red- and white-tubered plants the 

 quality of the pigment being constant, it is the quantity that varies 

 and that is not readily to be measured. In one family of 100 seedlings 

 I ascribed values to the colour as seen in the stem. The parent was a 

 plant with a medium quantity of pigment in the stem. The degrees of 

 pigmentation in the stems of the seedlings were divided into " strong," 

 " medium," and " weak," and the numbers in each class bore to each 

 other as nearly as possible the relation of 1 strong : 2 medium : 1 weak. 



The absence of distinct and definable gradations between the various 

 degrees of colour, as well as the possible personal bias in the classifica- 

 tion, is my reason for not publishing the results of the observations on 

 colour in stem and foliage which were made in every individual plant 

 during the four years' work covered by this paper. 



Observations on the colour of the flowers have been made, but only 

 in the case of seedlings of the potato known as Lindsay's etuherosum 

 has anything of interest been observed : a description of the phenomena 

 in the flowers is given in the section dealing with this peculiar variety. 



Observations on the pollen have disclosed some interesting facts in 

 connection with heredity of sterility and have confirmed East's (4) 

 observation of the relation between amount and viability of pollens. 



The incidence of disease {Phytopthora infestans) has been closely 

 watched, but only in the case of the Lindsay etuber, q.v., has anything 

 definite been observed. 



The fact that there has been till now no really immune variety to 

 work with has prevented any headway being made in this direction. 



The Material used. All the observations, excepting those dealing 

 with the peculiar variety already described by Sutton (8), and known 

 as Lindsay's etuherosum, have been made with ordinary domestic 

 varieties. The most useful of all the potatoes employed has been 

 Sutton's " Flourball," which indeed gives the key to the understanding 

 of them all. The black pigment was introduced by the potato known as 

 the " Congo," a potato which is of a deep blue-black both within and 

 without and which is used domestically for salads. One variety which 



