18 



TEANSLOCATIOIT OF PLANT FOOD IN" WHEAT SEEDLINGS. 



radicles grown in water culture, however, contain only half as much 

 potash as those grown in the complete medium. At the end of the 

 experiment, wliile the weights of the radicles grown in water and the 

 amounts of potash are about the same as for the radicles of the nutrient 

 solution, the amounts of nitrogen and phosphoric acid are less for 

 the former than for the latter. The differences are not, however, 

 very great in any case, thus indicating that the rootlets up to this age 

 do not retain the plant food absorbed. Comparing the plumules, 

 those grown in distilled water contain about one-half as much nitrogen, 

 one-third as much phosphoric acid, and not quite one-fifth as much 

 potash as do those grown in the nutrient solution. 



Of the inorganic constituents found in the axes of the seedlings 

 grown in a nutritive solution, the following proportions occur in the 

 plumule: 



Table 4. — Percentage of inorganic constituents of the axis that occur in the plumule. 

 (Seedlings grown in complete nutritive solution.) 







Phos- 







Age. 



Nitrogen. 



phoric 

 acid. 



Potash. 



Weight. 



Days. 



Per cent. 



Per cent. 



Per cent. 



Grams. 



3 



42 



42 



36 



37 



5 



56 



53 



68 



50 



7 



67 



60 



80 



50 



9 



70 



72 



89 



66 



12 

 15 



72 

 72 



76 

 79 





67 

 71 



94 



The complementary percentages are, of course, the amounts found 

 m the radicle. Here again it is seen that potash is rapidly stored up 

 in the plumule, at a much faster rate than the weight increases or 

 than the nitrogen and phosphoric acid accumulate. 



Just why the seedling absorbs potash with such avidity and accu- 

 mulates it so rapidly in the plumule is at present a matter of mere 

 conjecture. At this early stage of development starch destruction 

 in the seed is marked, and there is equally great activity in starch, 

 sugar, and fiber formation and elaboration in the plumule. It is 

 not at all improbable that through centuries of successful combat 

 the plant has acquired this fixed characteristic which has proved its 

 salvation, namely, the accumulation of plant food, especially of 

 potash at an early stage, thus placing itself in a position later to 

 elaborate its own food material with the aid of the sun's rays and 

 the carbon dioxid in the air. 



Before concluding the consideration of the inorganic constituents, 

 some mention of similar work done with ordinary beans {PJiaseolus 

 vulg.), and lima beans {PJiaseolus lunatus) may be of interest. The 

 results obtained with these seeds show less regularity, however, 

 because it is more difficult to obtain samples of such uniformity as 



