140 Plant Physiology 



same variety a marked difference will result when plants 

 grown in Michigan, for example, are compared with those 

 grown on alkali land under irrigation in Colorado. It is 

 to be expected, therefore, that there will occur considerable 

 variation in the ash under different conditions of soil 

 water, fertilization, temperature, and light, or under any 

 conditions affecting transpiration and growth. 



75. Ash content at different ages. - - It is of interest to 

 note that at different stages of growth the rate of absorp- 

 tion of mineral nutrients and nitrogen bears no constant 

 relation to body weight. Arendt, 1 Bretschneider, 2 and 

 others have shown that in general ash and nitrogen are 

 present in the young plant in relatively greater quantities 

 than in later stages of growth ; while starch accumulates 

 relatively more rapidly in the maturing plant. Each of 

 the observers referred to employed oats, and they divided 

 the growing period into five intervals practically as fol- 

 lows : (1) as three to five leaves are unfolded, (2) some- 

 what previous to full heading, (3) plants in full blossom, 

 (4) beginning of ripening period, and (5) complete matur- 

 ity. In these experiments the roots were not taken 

 into consideration. The table on the opposite page 

 from Bretschneider shows the absorption of total ash 

 and of nitrogen during different stages. With respect to 

 the absorption of individual constituents, phosphoric acid 

 is obtained in relatively greater quantity during heading, 

 while potash is more rapidly absorbed during the early 

 stages, according to Arendt. 



Arendt, " Wachsthumverhaltnisse der Haferpflanze." Jour. f. prakt. 

 Chem., 76 : 193, 860. 



2 Bretschneider, " Das Wachsthum der Haferpflanze." Leipzig, 1859. 



