22 Genetic Studies in Potatoes 



In 1906 the variety Queen of the Valley was fertilized by Flourball. 

 One of the ^i seedlings was fertilized in 1908 by a seedling arising 

 from a selfed ball of Bohemian Pearl. This gave rise to a family which 

 was grown in 1909, one of whose units (il/5 535) was grown on in 

 Barley in 1910, selfed in that year, and the seed sent to Cambridge 

 University Farm for raising in 1911. The parent plant dropped out of 

 culture. 



After the seedlings had been planted out a short time it was obvious 

 that the whple family were exhibiting a character which had not been 

 met by us in any of our cultures. The stems, instead of standing erect, 

 lay along the ground, creeping centrifugally so that as the plant became 

 fully grown a varying area averaging not far short of a square yard 

 would be closely^ covered by a fresh, healthy, green mass of foliage 

 (Plate II, fig. 5). When handled the stems themselves felt like soft 

 rubber tubes, which led to the natural inference that they simply lay 

 on the ground because they could not stand up. The number of nodes 

 and mode of branching was of the usual type, but the leaves all pressed 

 upwards towards the light so that a well-developed plant of this type 

 formed a flattened green cushion on the ground. The terminal leaflets 

 turned towards the light, but the stems did not turn up vertically 

 except at their extreme distal ends. This characteristic habit of growth 

 has persisted, as will be detailed later, both in selfed cultures and in 

 the vegetative successors grown from tubers. Nor indeed is this change 

 of habit to be seen only after the stage of planting out. The seedlings 

 when but 2" in height show a tendency to collapse, and at a little 

 later stage the whole seedling plant tends to flatten out (Plate III, 

 fig. 1). 



The habit of growth just described we have termed the " prostrate " 

 one, and in this paper a " prostrate " stem means a stem from plants 

 with this peculiar habit of growth. 



One feature which was particularly obvious in 1911 (a year of great 

 drought) was that the ground underlying all these plants was moist, 

 whereas the surrounding area was hard and cracked. This feature will 

 be referred to later. 



A more or less upright character of the potato haulm is axiomatic 

 amongst potato growers, who invariably look askance at any variety 

 whose haulm tends to spread or flop. The stems of many varieties, 

 however, on reaching maturity, tend to fall groundwards, but this is 

 entirely different from the "prostrate" condition that has just been 

 described. In these cases it is the excessive weight of the haulm and 



