28 The Living Plant 



composition is concerned, simply in the proportions of the in- 

 corporated water, though this tells by no means all of the story; 

 but it helps to explain why thej^ are so easily transformable by 

 the plant one into the other. Taken together the facts suggest 

 the probability that one of the three is a first-formed or basal 

 substance from which the others are transformed. In a general 

 way chemical research sustains this hypothesis, and points to 

 grape sugar as the usual basal substance first formed in the light 

 in green leaves. For all of our purposes, therefore, we may accept 

 grape sugar as the conventional basal photosynthate, and its 

 formula (Cg H^g Oq) should be fixed by the reader in his memory 

 as another of the valuable conventional constants. 



It may seem to the reader just here that in treating this sugar so 

 fully, I dwell overlong on a point of only subordinate value. But 

 in this my critic would err, for, as a later chapter on the subject 

 will show in detail, this photosynthetic grape sugar is the material 

 from which, with certain transformations and some additions, 

 plants make all of their substance and special materials, includ- 

 ing their protoplasm, and derive all of their energy for work; in 

 other words, it is their food. And since animals all take their 

 sustenance, whether directly or indirectly, from plants, it is the 

 basis of their food also. These facts may conveniently be brought 

 together, even though somewhat in advance of all of the evidence, 

 in this generalization, which constitutes another of the great 

 botanical verities, — that the photosynlheiic grape sugar formed 

 in green leaves in the light is the basal food of both ylants, and ani- 

 mals. This sugar is therefore one of the three most important 

 substances in organic nature, chlorophyll and protoplasm being 

 the other two. 



Our next task is sufficiently obvious; we must find the source of 

 supply of the materials entering into the composition of the sugar, 

 which, the reader will remember, is an addition • to the plant. 

 Now a scrutiny, from this point of view, of its formula, viz., 

 CgHiaOg, at once reveals the suggestive fact that the H and the O 



