190 



Joiinial of Agriculture, Victoria. [10 March. 191 2. 



While the composition of the ash of the whole crop varies according- 

 to the soil it is grown on, it is evident that the crop exercises to some extent 



a power of selection, absorb- 

 ing in largest quantity those 

 particular constituents which 

 it requires : — Thus the ash 

 of wheat contains a rela- 

 tively high percentage of 

 phosphoric acid and a low 

 percentage of lime. The 

 ash of mangolds, on the 

 other hand, is rich in potash, 

 whilst that of clover and 

 lucerne is rich in lime. What 

 probably happens is that the 

 nutrient solution for any 

 given soil is more or less of 

 constant composition. The 

 root hairs allow this soil 

 solution to enter by osmosis 

 until the concentration inside 

 the cell is the same as that 

 17. EPIDERMIS OF FED-RATION WHEAT ^^j^j^^^^^ No mote Can enter 



(under SURFACE OF LEAF) SHOWING ^^^^-j ^j^^ jj^^j^^g ^^jj^ ^f ^^^ 



STOMATA (3321 PER SQUARE CENTi- ^^^^^^ withdraw some of the 

 metre). nutrient solution for con- 



structi\'e purposes and thus lower the concentration of the cell sap in that 

 ingredient. Soda is more abundant in the soil than potash, yet in the ash 

 of wheat potash is far 

 more abundant than is 

 soda. 



In the case of wheat 

 the plant cells keep utiliz- 

 ing the potash for the 

 construction of tissue and 

 thus low^ering the concen- 

 tration and permitting 

 more to enter. On the 

 other hand very little 

 .soda is used by the plant 

 cells and the cell sap is 

 therefore as concentrated 

 in soda as that of the soil 

 solution. 



Storage and Migration 

 OF Food. 

 The leaf is the manu- 

 facturing organ of the 

 plant. It has already 

 been shown that it is re- 

 sponsible for the forma- 

 tion of carbohydrates such as starch and sugar from simple inorganic 

 materials. It also builds up organic compounds containing nitrogen such 



epidermis of leaf (x 300) OF WHEAT 

 SHOWING STRUCTURE OF STOMATA. 



