74 



CHANGES OF COMPOSITION 



[chap. 



are too valuable to be cast aside in the dead leaf, and 

 are therefore carefully removed into the permanent 

 storehouse of the stem and roots during the winter 

 resting period. 



In herbaceous plants, which die down to ground level 

 each winter, the roots form the storage organs ; the stem 

 and leaves are depleted of their valuable constituents 

 before death sets in. For example, Table X. shows the 



Table X.— Material contained in Upper Growth of Hop- 

 Plant AT TIMS OF Picking and after Dhng Down. 

 Lb. per Acre. 



material contained in the parts of a hop plant above 

 ground (i) at the time of its maximum growth when the 

 hops — t.e. the seed vessels — were fully formed ; (2) after 

 the hops had been picked and bine and leaves were dead 

 down to ground level, and from the table it will be seen 

 that about one-half of the nitrogen, one-half of the 

 phosphoric acid, and nearly all of the potash contained 

 in stem and leaf are removed and sent down to the root 

 for storage before the winter resting period sets in. 



Similar cases of economy, storage, migration, and 

 retranslation may be traced everywhere in the life- 

 histories of plants, the guiding fact being the endeavour 

 of the plant to ensure its continued life and reproduction 

 by providing a sufficient food supply to start either the 

 next generation (the seed) or the next phase (in the 

 case of plants reproducing asexually by bulbs, suckers. 



