THE WHEAT GRAIN AND PLANT 19 



silica. They, too, are reduced. If there is an abundance of 

 rain, the cells continue work long, elaborate much vegetable 

 matter, and the plant grows. 



If the water supply is insufficient and the soil parsimonious, 

 this prodigious consumption cannot be supplied, and dessication 

 of organs takes place. This begins in the oldest leaves, and 

 nearly always the little leaves at the base of the stem become 

 soft, flabby, and withered. Analyses have been made which 

 show that these leaves let escape some nitrogenized matter, 

 phosphoric acid and potash, which they contained when living, 

 green and turgescent. Thus the closing of one of these groups 

 of little cell factories by the dessication of a leaf is a very 

 important process to the plant, for less vegetable matter is 

 elaborated than if it had continued its work. In dry years a 

 shortening of the stems and a comparatively small amount 

 of straw results. 



The dying of leaves involves not only the closing of these 

 workshops, but the transportation of much of the finished 

 product stored in them. Metamorphosis of the nitrogenized 

 matter which forms the protoplasm, the living part of the 

 cell, takes place, and it assumes an itinerant property which 

 enables it to pass through membranous walls and migrate 

 over the liquid highways to new leaves. With it are carried 

 phosphoric acid and potash. Some of the elaborated material 

 is thus continually being transported from lower to upper 

 leaves during the entire period of vegetation. Flowering takes 

 place when enough material has been elaborated to nourish the 

 appearing seeds. This migration of substance can take place 

 only when there is plenty of water, and the crop fails when it 

 is too dry. Too much water is also injurious, for it causes a 

 tendency to keep up growth indefinitely. The Minnesota sta- 

 tion found that the wheat plant produced nearly one-half its 

 dry and three-fourths its mineral matter by the end of 50 

 days. This included 75 per cent of the potash, 80 per cent 

 of the phosphoric acid, and 86 per cent of the nitrogen. At 

 65 days, 65 per cent of dry and 85 per cent of mineral mat- 

 ter had been produced, as well as most of the fiber, which suf- 

 fered a loss after 81 days. 1 Compared with the processes ob- 

 served in nitrogenized matter, phosphorus and potash, the 

 1 Minn. Bui. 29. pp. 152-160. 



