GENETIC STUDIES IN POTATOES. 

 THE INHERITANCE OF AN ABNORMAL HAULM TYPE. 



By R. N. SALAMAN, M.A., M.D., Cantah., 

 AND J. W. LESLEY, M.A., Cantab. 



(With Plates II— V.) 



The varieties of potato haulm, whose anatomical and genetic relations 

 are described in this paper, arose in the garden of one of us^ at Barley, 

 Hertfordshire. From the years 1906 to 1911 it had been the habit to 

 train all the experimental seedlings raised in this garden up to horizontal 

 wires placed 9" and 18" respectively above the ground. To these wires 

 the haulms were loosely tied. In 1910 a line of plants, situated some- 

 what closely to a row of apple-trees, showed a uniform tendency to 

 commit suicide, i.e., the stems would grow quite healthily till they 

 attained a length of about 2 ft 3 ins by which time the last 9 inches of 

 growth, instead of continuing its upright habit, would bend abruptly 

 downwards and then the stem would get constricted or nipped at the 

 point to which it was tied to the top wire. Other families, when not 

 tied to supports and not in a shaded situation, often exhibited amongst 

 their members examples who soon adopted a sprawling habit, but 

 directly they had adopted this secondary position the terminals of the 

 haulms would all take a fresh vertical direction. This variety will be 

 discussed later. 



Consideration of this family of plants gives rise to the conception of 

 a potato whose haulm had an inherent desire to lie down rather than 

 stand up. Later on in the season the true reason became manifest, 

 viz., that the plants were tending to grow towards the light from which 

 they were obscured by the apple-trees. The conception, however, 

 remained, and by an extraordinary coincidence found a genuine basis 

 in our cultures in 1911. 



1 B. N. Salaman. 



