4 BULLETIlir 958, U. S. DEPARTMENT OF AGHICIILTTJBE. 



results showed an average gain in weight after the death of the foliage 

 of 26.4 per cent, or 57 bushels per acre. 



DESCRIPTION OF THE TUBER-BEARING PARTS. 



The tubers are borne on underground stems, commonly called 

 stolons, which are modified branches arising from the nodes of the 

 main stem and situated below ground. The development of the buds 

 into stolons rather than leaf-bearing branches depends largely upon 

 certain definite environmental conditions, chief among which is the 

 exclusion of light. De Vries (10) maintains that each axillary bud 

 of the stem of a potato plant has the capability of developing, accord- 

 ing to the conditions which surround it, into either a leafy stem or a 

 tuber-bearing stolon. This is further substantiated by Franz (2), 

 who states that if the lower buds are exposed to the light green shoots 

 will generally develop instead of stolons, likewise the upper axillary 

 buds will develop into stolons instead of green shoots if light is ex- 

 cluded early enough. 



The arrangement of stolons on the stalk is in general five ranked, 

 though there are many exceptions to this, which are attributed to the 

 failure of some nodes to develop. This same arrangement occurs with 

 the leaf scales on the stolons. The stolons terminate with leaf scales 

 which are strongly recurved, usually at an angle between 90° and 180°. 

 No law has been observed by the writer governing the direction of the 

 recurving. 



' The stolons start comparatively early in the growth of the plant, 

 usually within a week or ten days after the plants have appeared 

 above ground, the stolons of the early varieties appearing a little in 

 advance of those of the late ones. Under normal conditions of 

 growth the stolons should be well started by the time the plants have 

 reached a height of 4 inches. 



The length of the stolons is subject to great variations, ranging from 

 less than an inch to lengths equaling or occasionally exceeding 18 

 inches. While there is much variation within the variety, and, in 

 fact, in the individual plant, there is a fairly well-defined relationship 

 between stolon length and variety, e. g., the Early Ohio is character- 

 ized by very short stolons, while, on the other hand, varieties are 

 occasionally found in which the stolons extend over such a wide area 

 as greatly to increase the work of digging. (Figs. 1 and 2.) 



DETAILS OF THE EXPERIMENTS. 



EXPERIMENTAL METHODS. 



The material used for the experimental work was grown under 

 field conditions, the cultiu-al practices employed following those in 

 general use in the locality in which the work was done. The digging 

 operations were performed by hand, special care being taken to get J 



