yo Journal of Agricultural Research v,.i. xviii. no. a 



contained in the plant approach the magnitudes present at complete 

 maturity. The potassium content may even be greater than at maturity. 

 The beginning of the second phase is indicated not merely by a decreased 

 rate of absorption as in maize but by definite and substantial losses of 

 certain consitutients (notably potassium and nitrogen and apparently 

 calciunO from the portion of the plant growing above the ground, and 

 prcsumablv from the entire plant. This loss takes place concurrently 

 with the migration of the same constituents into the developing heads. 

 The end of the second phase is characterized by a tendency to absorb 

 again the soil constituents previously lost. This tendency may result 

 in taking up considerable quantities when the plants are very large and 

 well developed, as in the 191 7 experiment. The third phase, occurring 

 at the time of ripening of the grain, is marked by a practically complete 

 cessation of absorption of all constituents and an actual loss of most 

 of these. 



The more significant facts brought out here would appear to be: That 

 the two elements with which plant g^o^vth in general is most closely 

 associated may approach or exceed their maxima at a comparatively 

 early stage of the plant's dcNelopment — that is, at the begimiing of head 

 formation; that absorption of potassium and nitrogen during the first 

 period of growth is approximately proportional to the growth attained, 

 and in the succeeding periods the final dry-matter content of the crop 

 more than doubles without any very substantial increase in nitrogen 

 content and with an actual loss of potassimu; furthermore, that the final 

 dry-matter content of the crop, even when it \-aries as much in yield as in 

 the cases reported, appears to be nearly proportional to the fresh weight 

 of the crop at the end of the first period. A direct relation is thus traced 

 between the amount of dry matter in the final yield and the amounts of 

 potassium and nitrogen absorbed in the first stage. 



The fact that nitrogen and potassium tend to leave the plant just after 

 the heads begin to fonn does not prove that their presence is inimical to 

 head fonnation (no actual losses occur in maize, for example), but indi- 

 cates rather that continued absoqition at this stage is probably incom- 

 patible with normal development. 



The explanation of the mechanism b\- which losses of certain constitu- 

 ents take place from gro\\-ing plants at an early stage of growth must 

 await further detailed studies and a considerable advance in our knowl- 

 edge of plant tnetabolism and particularly of the forms in which the 

 various elements exist in the cell sap during the period of translocation 

 to the heads. We shall content ourselves here with the suggestion that 

 such losses are probably due to complex but purely physical causes, a 

 suggestion rendered plausible by the simultaneous occurrence of low 

 concentrations of the water extracts and the movement of mobile con- 

 stituents from the leaves to the heads. 



