248 



WATER-CULTURE. 



amount depending somewhat "upon the temperature at which 

 the ash is prepared." In the following short table a few of the 

 manj- analyses collated by Johnson ^ have been brought together 

 to exhibit the proportions of the ash constituents. 



6G6. The foregoing table indicates that wide divei-sity exists 

 in the amounts of the ordinary ash constituents of common 

 plants. But comparison of a lai'ge number of analyses shows 

 that the following general statements may be made : — 



1. Plants which closel3' resemble each other in structural 

 characters have substantially the same proportions of ash con- 

 stituents. 



2. The proportions of the ash constituents in anj- part of a 

 plant may var^' within certain limits ; and these limits ma}- differ 

 at different periods of growth. 



3. The proportions may var^' widely for differeut parts of the 

 same plant. 



667. Not onl}' are the elements enumerated in the first list in 

 665 always present in the ash of flowering plants, but they are 

 shown by experiment to be indispensable to their full develop- 

 ment ; and there is a reasonable certainty that iron, sulphur, 

 and probablj' chlorine, should be placed in the same category of 

 indispensable elements. 



According to Nageli,^ some of the flowerless plants, notably 

 the moulds and the schizomycetes, can attain full development 

 with fewer elements. 



WATER-CULTURE. 



668. Apparatus. While chemical analysis of the ash of plants 

 reveals the character of the mineral matters which they absorb 

 from water and soil, it cannot materially aid the investigator in 



■■ How Crops Grow, 1868, p. 150. 



^ Sitzungsb. d. bayer. Akad., 1879, p. 340. 



