280 
On the Cultivated Potato. 
to say, there is nothing of the kind that I know of in a clear,, 
comprehensive and popular form and to practical men it is a 
mvsterv : there is a manifest want in this direction.* Physiology, 
1 need not explain, is that department of natural science which 
treats of the organs of animals and plants. The plant is con- 
stituted in three parts ; radical fibres or roots proper, stolons 
stems, or haulms, as we call them, and the tuber. The radicaJ 
fibres are the only true roots, and to seek for nourishment for 
the plant they traverse the soil far and near. A potato tuber is 
in fact an underground branch, the eyes of the potato are really 
buds ; a tuber, then, is a portion of the stem of the plant in 
which the tissues become thickened and filled with nutritive 
matter. Propagation by tubers is not properly reproduction, 
but plant division, and sooner or later existence in this way 
must end. A healthy plant is said to have at least ten sets of 
main roots, four to a set, nearly, if extended end to end, one- 
third of a mile long, with innumerable mouths or absorbents, 
say, 25,000, all seeking inorganic matter and water. The 
practical conclusion from this is that the common potato 
{S. tuberosum) is designed for a dry, very dry, soil and 
climate. The tuber, so far as Nature is concerned, is constructed 
only or chiefly for the purpose of propagation : all the plant 
resides there in embryo, together with a store of suitable food, 
and the tuber is perfect when no larger than a pea. The roots 
supply water and earthy salts, to enable the leaves to decompose 
the carbonic acid absorbed by them from the air. Suppose^they 
absorb more than the leaves can exhale, then the plant is 
weakened and water-logged. Liebigf says the motion of the 
sap is caused by atmospheric pressure and transpiration from the 
leaves ; a loaded atmosphere suppresses transpiration, stagnates 
the sap, and so induces the putrefaction which delights the 
hovering clouds of fungi-spores or seeds. The potato and the 
hop, according to Liebig, are especially liable to suffer from im- 
peded transpiration. The same atmospheric influences cause 
influenza in the human subject, by checking the action of 
the skin ; and curiously enough it is commonly observed in 
1 orkshire that potato-disease and influenza in horses came the 
fniit. Tubers are a reserve store of nutriment for a plant to draw upon when it 
cannot get food from other sources, as a tradesman draws upon liis investments if 
he wants to extend liis busine.-'S. If the potato cannot got its food, or cannot 
digest it like any other organized being, it will fiill ill. If tlio leaves are killed 
by fro.st, for instance, it, will be unable to digest its food; and if they are attacked 
and disorganised by fungi, th(! result will be the same. — J. G. B. 
* Mr. Chalmers Morton, to wlioin we are indebted for many things, has given 
us in his 'Handbook of the Farm Series,' a useful little work, 'riant Life,' bj- 
JFnxwell T. Masters, F.R.S.. in which there are six references to the potato. 
.» t ' Motions of Fluids in Animal Body.' 
