lo March, 1912.]^ W/nat and its Cultivation. 191 



as the proteins. The intermediate stages between tlie absorption of nitrates, 

 sulphates, and phosphates by the roots and the elaboration of proteins by 

 the living cells of the leaf are not known, but it seems probable that inter- 

 mediate products like asparagine and other amido acids are first formed and 

 that these are subsequently elaborated intO' protein. Most of the compounds 

 elaborated by the leaf are used for building up new cells, cell walls and in 

 nourishing the living tissue. During active vegetation and under ordinary 

 conditions of growth there is more material constructed than is needed for 

 the immediate requirements of plants. In tHe case of wheat .sown in April 

 or May the early growth is usually vigorous. As winter comes on the 

 temperature of the soil gradually, lalls and growth appears to be at a 

 standstill. 



In reality, however, assimilation is going on actively but the products 

 are utilized in the formation of new roots and the ultimate success of the 

 crop is in a large measure dependent on the nature of the root system 

 built up in this stage of apparent inactivity. With a gradual rise of 

 temperature characteristic of early spring the wheat plant enters on the 

 most vigorous period of its existence. Assimilation now proceeds actively 

 and the products move off as fast as they are produced and are stored 

 in the stems of the plant for future use. At a later stage the lower leaves 

 begin to die off, and the carbohydrates together with the important nitrogen 

 phosphoric acid and potash compounds are gradually moved to- the more 

 active portions of the plant. 



After the fertilization of the grain take.s place the absorption of food 

 supplies from the soil practically ceases and the whole energies of the 

 plant are concentrated on the migration to the grain of the already 

 elaborated material stored in the leaves and stem. 



There is a general movement of water from the lower portions of the- 

 plant to the upper parts, and with the moisture the sugars, amides and 

 proteins are transferred to the grain. Desiccation now sets in, and in the 

 case of wheat about two-fifths of the whole dry matter of the plant is found 

 in the grain. Of the nitrogen and phosphoric acid found in the whole plant no 

 less than three- fourths of the former and about two-thirds of the latter 

 substance are found in the kernel. 



The microphotographs and sections illustrating this article were pre- 

 pared b\- the Acting Vegetable Pathologist, Mr. C. C. Brittlebank. 



{Fo he continued.) 



