The Potato. 69 



diseased sets, as from those sets where no taint or disease could 

 be discovered. 



And here, in order to elucidate this matter, it becomes neces- 

 sary to investigate liow and in ichat icay the j)otato is formed. 

 tSome dry and clean potatoes v/ere placed on a chimneypiece in 

 :i seldom-used room. In due time they threw up stalks, short, 

 thick, and studded with minute leaves, whilst on the summit of the 

 stalk were three or four larger but still minute leaves, forming a 

 tuft. Speedily from the axils of the minute leaves on the stems 

 a shoot was thrown forth, terminating in two leaves, closely en- 

 wrapped the one by the other. It was the germ of the future 

 potato, whose formation can by any one be rendered evident : 

 the inner leaf forming opparcnihj the cells of the jiotato in 

 Avhich the starch is deposited, whilst the enwraj)ping leaf forms the 

 skin. This experiment has been witnessed by so many persons 

 as to leave no doubt of its accuracy. When the tuber-producing 

 shoot is about 2 inches long, it becomes easy to introduce it into 

 a large bunch of soft moist moss, and in ten days or a fortnight 

 a minute potato, not larger than a duck-shot, will be found in- 

 stead of the two terminal leaves ; and this experiment can be 

 Aaried. By changing the position of the potato, one of the afore- 

 said shoots can be induced to become the future stem of the 

 plant, whilst the stem, as originally intended, can be made to 

 produce a potato at its extremity. It may also be observed that 

 these productive shoots from the axils of the vdnute leaves, if cut 

 iiicay, are never reproduced from that axil ; and it is very possible, 

 with cai"e, to cut away every one of them. That being done, the 

 stem grows rapidly, and becomes long, branchy, and strong. If, 

 now then, you lay down the stem — or, leaving it erect, you keep 

 it moist and deprive it of light — you will obtain a potato from the 

 usil of every leaf above the deprived portion ; white, if kept in 

 the dark ; partly wliite, partlv coloured, if partially sliaded ; and 

 a dark puiplish green, if exposed to the light. A damp or moist 

 place is necessary ; and frequently on these tubers a short strong 

 shoot, with the two terminal leaves, may be seen ; ready, if cir- 

 cumstances be favourable, to produce a second tuber ; and as the 

 stem Avhere it proceeds from the eye of the tuber is more or less 

 -of a reddish purple, it has led to the mistake so often insisted on 

 hy many, " that the disease often or ahvays orif/inates in the 

 ioicer -portion of the stem where it adjoins the set. It is, however, 

 ■(juite a delusion. 



IV. Can tlie disease he artificialhj induced or prevented^ — A large 

 t)-light melon-frame was so placed that along its southern front 

 large " Irish blue " potatoes were planted, 8 inches deep from the 

 surface, the first week in February, in 184H, 1847, and 1848. 

 When the plants made their appearance they were exposed, 



