432 Development of Roots of Agricultural Plants. 
for great part of the year, vitality Avill be sustained by tempera- 
ture derived from the deep-seated rootlets. 
In -nlieat-cultivation the great object is to multiply the lateral 
rootlets as much as possible, that they may avail themselves of 
the more abundant nutriment towards the surface of the soil. 
One great end obtained by pressing the ground in light soils 
before the sowing of wheat is the encouragement of laterals. It 
is true that wheat will sometimes penetrate to a great depth, but 
seldom perhaps with advantage. 
We now come to the third stage, in which roots or portions of 
them become reservoirs of nutriment for future use. Roots vary 
considerably in their character : some penetrate deeply, remain- 
ing fibrous and delicate to the end ; some throw out numerous 
laterals, and affect the surface of the soil ; some merely yield the 
necessary daily nutriment ; while others, under various guises, 
as asparagus, turnips, carrots, 6cc., devote certain of their parts 
or ramifications to the especial office of storing up starch, pectine, 
bassorine, and other nutritive matters, sometimes in enormous 
quantities and with'eitraordinary rapidity. 
We must not, however, suppose that all underground parts 
which serve as storehouses belong to the same category. The 
bulb of the onion, the corm of the saffron, the tubers of potatoes, 
though answering the same end, are either furnished by the base 
of the leaves or are underground stems. The trunks of trees 
themselves are also in many cases receptacles of nutritive 
matter, of which the sago-palm is a well-known example, and 
the lime, abounding in mucilage, one nearer at home. In a 
great variety of plants, moreover, the pith supplies a large, 
though temporary, supply of nutriment. The cells, however, for 
the most part, are soon exhausted, and become mere bags of 
air. Sometimes there is a double store of nutriment, as in some 
species of crocus, both in the corm and thickened roots. 
It would be wrong, however, to suppose that the proper func- 
tion of roots in general is that of storehouses. Their office is 
rather to convey fluids which, either in their course through the 
roots themselves, or the stem with its ramifications, or finally 
the leaves and bark after various elaboration, deposit various 
matters which are either set aside as of no further use, or where 
they can do no harm, as the crystals which are so abundant in 
many plants, or stored up carefully to serve some ulterior end. 
In some plants, like carrots and turnips, the main object- 
seems to be the deposit of nutriment for the perfection of the 
seed in the ensuing year ; while in the case of perennials, either 
A special part is devoted to this purpose, as in many orchids, 
whose place when it has become effete is supplied by a new 
growth, or the supply is generally distributed and used as occa- 
