24 The Living Plant 



latter experiments, however, special appliances and methods 

 are necessary; and these are fully described in the various works 

 devoted to experimental plant physiology, and mentioned in the 

 preface to this book. 



If the reader should experiment at all widely upon this matter 

 of starch formation in leaves, he will sooner or later come upon 

 kinds which exhibit no starch whatsoever, even under perfect 

 conditions of light. Chemical analysis, however, always shows 

 this fact, — that such leaves contain an equivalent amount of 

 some sugar. Moreover, and this is a matter of consequence, 

 analysis shows also that even the starch-forming leaves contain 

 a sugar, and that, furthermore, it is from this same sugar the 

 starch is made. We come therefore to a generalization of the 

 greatest phj^siological consequence, the second, in fact, of the 

 great botanical verities, and one which the reader should fix deep 

 in his memory and incorporate with his visualized image of the 

 working green plant, that plants containing chlorophyll make in 

 the light a sugar which is commonly transformed into starch. The 

 process being one of formation, or synthesis, under action of 

 light, is called scientifically photosynthesis, while the substance 

 made is the photosynthate. 



It will sooner or later occur to the reader to ask, especially 

 if he has tried these experiments for himself, whether this photo- 

 synthetic sugar is simply a transformation of something already 

 existent in the plant, or a new substance that has been added 

 thereto. This can be settled by the conclusive test of compara- 

 tive weights; for, obviously, if it is a transformation, photo- 

 synthesis would not be accompanied by increase in weight while 

 if a new substance it would. It is with difficulty that I resist 

 the temptation to describe to the reader the simple but highly 

 satisfactory methods and instruments by which this important 

 matter is experimentally determined; but my book has limits, 

 and besides I am well aware that any attempt to exhaust my sub- 

 ject is likely to produce a similar effect on my reader. So I must 



