160 



HOW CROPS GROW. 



By reference to the table, (p. 152,) it will be observed 

 that the pea and bean kernel, together with the allied vetch 

 and lentil, (p. 379,) also nearly agree in ash-composition. 



So, too, the ashes of the root-crops, turnips, carrots, and 

 beets, exhibit a general similarity of composition, as may 

 be seen in the table, (p. 154-5). 



The seeds of the oil-bearing plants likewise constitute a 

 group whose members agree in this respect, p. 3T9. 



5 1 The ash of the same species of plant is more or less 

 variable in composition, according to circumstances. 



The conditions that have already been noticed as in- 

 fluencing the proportion of ash are in general the same 

 that affect its quality. Of these we may specially notice : 



a. The stage of growth of the plant. 



b. The vigor of its development. 



c. The variety of the plant or the relative development 

 of its parts, and 



d. The soil or the supplies of food. 



a. The stage of growth. The facts that the different 

 parts of a plant yield ashes of different composition, and 

 that the different stages of growth are marked by the 

 development of new organs or the unequal expansion of 

 those already formed, are sufficient to sustain the point 

 now in question, and render it needless to cite analytical 

 evidence. In a subsequent chapter, wherein we shall at- 

 tempt to trace some of the various steps in the progressive 



