42 THE PLANT. 



case with the latter on germination, but is always re- 

 filled and keeps increasing in size. The perennial plant 

 always receives more than it expends; whereas the 

 monocarpous plant spends its whole store in forming 

 fruit. 



The fact that the roots of the turnip, in autumn, 

 grow at the cost of the constituents of the leaves, 

 readily explains the influence which the removal of 

 leaves will exercise upon the crop at different stages of 

 growth. The removal of a few leaves in August makes 

 no great difference to the root, while the removal of 

 leaves at the end of September causes the greatest dam- 

 age to the root-crop. Metzler, who made very accurate 

 comparative experiments upon this point, found that an 

 early cutting of the leaves reduced the turnip crop by 

 7 per cent, only, while a late, or a second cutting, re- 

 duced it by as much as 36 per cent. 



If, in the first year, instead of the turnips being re- 

 moved from the field at harvest, the tops were merely 

 cut off and the roots were left and ploughed in, the field 

 would, on the whole, sustain a loss of soil constituents ; 

 still the roots in the soil would retain the greater por- 

 tion of them. A very different relation would arise, if 

 at the end of the second year of vegetation the turnip 

 tops were cut off, and the stem were removed together 

 with the seed. For, at the end of the first year, the 

 root would still retain the far larger portion of the 

 azotised and also of the incombustible constituents, 

 which would thus be left in the soil ; but in the second 

 year these materials would be carried into the over- 

 ground part of the plant, and there be used for the 

 production of the stem and the seed; hence, the re- 

 moval of the latter would of course make the soil poorer, 

 even though the roots were now left in it. Before the 

 shooting and flowering, the root was rich in soil con- 

 stituents ; after the production of seed, its store of them 

 is exhausted. If the plant is cut off and the root left 

 in the ground, before flowering, the soil retains the far 

 greater portion of the nutritive matter which it had 

 given to the plant ; on the contrary, after flowering and 



