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Journal of Agricultural Research voi. xvni. No. » 



activity; the leaves are a vivid green; the tissues are moist; and 

 growth, measured in both weight and height, is considerable. The 

 second period is clearly one of a different kind of activity; structural 

 differentiation is taking place; and fully formed heads may be devel- 

 oped without any further increase in the growth of the plant, as is shown 

 in the 191 6 experiment when there was practically no increase in fresh 

 weight after the eighth week. The leaves lose their green and moist 

 appearance and the stems and leaves fall off in total weight whether 

 that of the entire plant is increasing or not. The third period, again, 

 is obviously different and is characterized by a loss of weight and by desic- 

 cation of all parts of the plant, accompanied by a more or less com- 

 plete loss of the green color of actively growing plant tissue. 



i& 17 



Pig 3. — Relation of growth of barley to absorption of potassium, nitrogen, phosphate, calcium, and mag- 

 nesium, for entire plant except roots. To emphasize the comparative differences in absorption of these 

 elements, the quantities actually found have been multiplied by 250. Experiment of 1916. 



When we consider the composition of the plant as represented by 

 the dry matter and water content (fig. 3, 4) no very obvious relation 

 is observed between the dry matter and the growth periods referred 

 to heretofore; the variation in water content is, however, quite consistent 

 therewith. This follows naturally enough from the fact that water 

 constitutes such a large proportion of the plant up to the last four weeks 

 of growth. The increase in the dry-matter content of the plant is 

 represented by a fairly straight line, the only considerable break being 

 in the plants from the more productive soil near the end of the season 

 when there was an absolute loss. 



The water content shows considerable variation^, indicated by very 

 sharp breaks in the lines at the beginning and end of the second growth 

 period. The first of these breaks appears to be particularly significant 

 because the soils were being maintained at that time at constant 



