DIFFERENT PERIODS OF GROWTH IX THE TURNIP. 25 



turned to account, from tlic want of this cooperation, no 

 fresh substances are absorbed ; in unfavourable weather, 

 the plant does not grow. No moi'e does it grow, even 

 though the outward conditions are favourable, if the soil 

 contains no proper nourishment. 



In the second half of the period of developement, the 

 roots of the turnip plant, having penetrated through the 

 arable surface deep into the subsoil, absorb more potash 

 than in the preceding stage. K we suppose that the 

 absorbing spongioles of the root reach a stratum of soil 

 poorer in potash than the upper layer, or not sufficiently- 

 rich in that material to yield a daily supply commensm^ate 

 with the requirements of the plant, at first, indeed, the 

 plant may appear to grow luxuriantly ; yet the prospect 

 of an abundant crop will be small, if the supply of the 

 raw material is constantly decreasing, instead of enlarging 

 with the increased size of the organs. 



In the economy of the turnip, the root receives during 

 the last month of vegetation nearly one-half of all the 

 movable constituents of the leaves ; and this constitutes, 

 after the completion of its first year's period of vegetation, 

 a store of organisable matter for future use. 



Durmg the spring of the following year the root begins 

 to shoot, putting forth a slight leafy top, and a flower- 

 stalk several feet high ; with the developement and 

 maturing of the seed, the plant dies. The chief bulk of 

 the food stored up in the root is applied, in the second 

 year or third period, in quite a different direction ; 

 though, beyond the mere supply of water, the soil seems 

 to take no part in this new act of life. 



All monocarpous plants — that is, all plants which 

 flower and produce seed but once — present, hke the 

 turnip plant, distinct periods of hfe, as regards the direc- 

 tion of organic activity in them. In the first, the plant 



