40 THE POTATO CROP. 



stances, and to rear its stem and leaves above the ground 

 in quest of organic materials of support. In the small, 

 immature tuber, planted whole and throwing up several 

 thin and sickly stems, it is obvious that the supplies of 

 food-materials must be greatly inferior to those of the 

 well-developed and well-matured tuber, which, being 

 divided into "sets," planted separately, secures also to 

 its young plants a greater range, both below and above 

 the soil, for carrying on its after processes of growth. 

 Indeed, so important is it for the health and vigorous 

 development of the crop that the plants should not be 

 too closely placed on the ground, that, even where whole 

 tubers are used, it would generally add greatly to their pro- 

 duce were directions given at the time of hand-hoeing the 

 drills to cut out the surplus plants, and only allow a single 

 stem, or at the utmost two, to remain attached to each plant. 

 The principles involved in the reproduction of plants 

 have been already discussed at p. 21, voL i., and although 

 the potato is not exactly reproduced from the seed, still its 

 mode of propagation is sufficiently analogous to be influ- 

 enced by the same causes as therein described. 



The quantities used per acre for planting vary much 

 in different districts, both when used whole or in "sets/' 

 Probably about 8 to 1 2 cwts. may be taken as the average 

 for the former, and from 6 to 9 cwts. for the latter mode 

 of planting. We have no well-authenticated field experi- 

 ments recorded in reference to the comparative production 

 of the two methods. In some experiments on a small 

 scale, and with another object (see p. 540, vol. i.), the 

 produce of the divided tubers greatly exceeded that of the 

 small tubers planted whole. 



Many growers are of opinion that the unripe tuber pro- 

 duces stronger plants than the fully-matured, owing pro- 

 bably to the proportion of starch being less, and that of 

 the inorganic substances relatively greater, than at a later 

 period of its growth. 



