12 THE CHEMISTRY OF THE FARM. 



stem, and stored up in the seed. If the season is a good 

 one, and the development of the seed fully accomplished, 

 the straw of the crop is left very thoroughly exhausted ; 

 while in a bad season it will retain far more of the materials 

 acquired during growth. For the same reason straw cut 

 while the crop is still green is far more nutritive than 

 when perfect ripeness has been attained. 



With a biennial or perennial crop the case is somewhat 

 different. The first development of root and leaf is the 

 same as in an annual ; but towards the end of summer 

 there is a storing up of concentrated plant food in the root 

 or stem to serve for the commencement of growth in the 

 following spring. In a biennial root crop, the turnip for 

 instance, the root attains a great size in autumn, the leaves 

 dying after transferring to the root their most important 

 constituents. The next season the root throws up a 

 flower stem, and the store of matter accumulated during 

 the preceding autumn is consumed in the production of 

 seed. With the production of seed the root is exhausted 

 and the plant dies. 



In trees plant food is stored up at the end of summer 

 in the pith, the pith rays, and in the layer between the 

 wood and bark. The leaves which fall in autumn have 

 lost nearly all their starch, albuminoids, phosphoric acid 

 and potash, these having been transferred to the stem. 

 By the action of the sun in spring-time the new buds 

 swell, the sap rises, the starch and other matters deposited 

 in the wood during the previous autumn are re-dissolved, 

 and employed at once for the production of new growths. 

 The sugar found in maple sap during spring results from 

 the transformation of starch stored up in the preceding 

 autumn. 



