112 PLANT LIFE ON THE FARM. 
fibrous portions, and the requisite secretions are stored 
the more readily in the roots. To ensure this rapid 
growth, more essential in an annual crop like potatoes 
than in those whose growth occupies part of two seasons, 
a warm aspect and a well drained soil are essential, while 
to ensure the formation of the secretions which render 
the plant valuable, free exposure to light is also requisite. 
Thus, hoeing and weeding owe their good effects not 
only to the removal of useless plants occupying space 
that might more profitably be employed, but they secure 
to the crop freedom from the shade of the weeds, and 
promote the access of light to the foliage and of air to 
the roots. The excessive action of the vegetative organs 
checks, to a varying extent, the development of the 
fruiting organs ; indeed, the object of culture is to keep 
the plant growing and to prevent its flowering. If the 
seed. of such plants is sown too early, growth is apt to be 
slow, and woody fibre is produced where succulent cells 
would be preferable, and, moreover, the tendency to 
produce flowers is enhanced by the high summer tem- 
perature which follows. If sown late, the growth of the 
vegetative organs is, for a time, rapid, because the soil is 
warmer and the sky lighter, while the tendency to form 
fibre and flower is checked. 
The formationgof subterranean tubers may be taken as 
an indication that the plant prefers a period of rest. 
The rest is, indeed, not absolute, but relative ; and while 
little external change may be visible, it is probable, and 
in some cases certain, that considerable chemical changes 
go on during the period of apparent inaction. Under 
natural circumstances the rest is secured, either by the 
.. occurrence of heat and drouth, or of a very low tempera- 
ture, the action of light being, in either case, excluded. 
These facts supply hints as to the proper mode of storing 
and pitting potatoes and roots. Moisture, light, and air 
should be excluded, the temperature kept as low as pos- 
