CLASS OF SOILS SUITABLE. 27 



dency to carry the growth of the stem below the surface 

 exists but to a comparatively small extent; even in raising 

 new seedlings from cultivated plants, their produce the first 

 year rarely exceeds the size of small birds' eggs, requir- 

 ing two or three more years of continued cultivation 

 to bring them up to the desired size. The enlargement 

 of the stem under ground is effected by the abnormal 

 development of its cellular tissue, existing naturally to a 

 small extent, but increased by cultivation; the vascular 

 tissue, however, is not susceptible of increase in bulk but 

 merely in length, running through the cellular tissues, what- 

 ever may be their development ; while the skin is capable 

 of any extension required to cover the increased size. 



The potato has a very wide range of soils, and also of 

 climates; it will grow, indeed, in almost any soil or 

 climate in which cultivation of any sort can be carried on. 

 We have just seen that it's native country lies within the 

 tropics, while we have already had occasion to remark (p. 97, 

 vol. i.) that its cultivation is carried on in countries even be- 

 yond the boundaries of cereal growth. The medium soils, 

 however, are those which it prefers the lighter class gene- 

 rally producing the best quality of potatoes, the heavier 

 class the largest crops. 1 On the soils of the different 

 sandstone formations large crops of excellent quality are 

 frequently seen, while the London market is largely 

 supplied with potatoes grown on the strong alluvial 

 soils of Yorkshire, and of Perth and Forfarshires. The 

 purely clay soils met with in the districts occupied by 

 the London clay by the weald and the gault clays in 

 Kent, Surrey, and Sussex, and by the oolite clays (Ox- 



1 In an experimental trial of the influence of soil in the yield of the potato, 

 it was found that the produce of four sets of the same variety, 

 Planted in a strong rich loam, weighed 34 Ibs. 

 light rich loam, ,, 29 



good gravel, 19 



sandy soil, ,, 15 ,, 



