35i THE WOELD OF LIFE 



Before leaving this brancli of my subject, 1 must say a few 

 words on the indications afforded by these varied products 

 of plant-life, of the absolute necessity of a directive power 

 and a mind of the highest organising intelligence for their 

 production. Quite as clearly, perhaps even more clearly than 

 for the development of the bird's feather or the insect's trans- 

 formations, does the agency of such a supreme mind seem to 

 be essential. 



Let us consider first the extreme simplicity and uniformity 

 of the conditions under which such marvellously diverse re- 

 sults are produced. A very large proportion of the vegetable 

 products useful to man are obtained from the tropical forests, 

 where the temperature is more uniform, the moisture more 

 constant, and the trees less exposed to wind than anywhere 

 else in the world. The whole organisation of the higher 

 plants is, as compared with that of animals, extremely simple, 

 and they are wonderfully similar in structure to each other, 

 even in distinct genera and natural orders. The roots, the 

 wood, the bark, the leaves, are substantially of the same type 

 in thousands of species. All alike build up their structures 

 out of the same elements, which they obtain from the water 

 and the few substances it dissolves out of the soil, from the 

 air and the carbonic acid and aqueous vapour it contains. 

 Yet under these conditions w^hat a seemingly impossible 

 variety of products arise. 



When the modern chemist attempts to bring about the same 

 results as are effected by nature in the plant, he has to em- 

 ploy all the resources of his art. He has to apply great heat 

 or great cold ; he uses gas or electric fires and crucibles ; he 

 requires retorts for distillation, and air-tight vessels and tubes 

 for the action of his reagents, or to preserve his liquid or 

 gaseous products ; but with all his work, carried out for more 

 than a century by thousands of earnest students, he has only 

 been able to reproduce in his laboratory a limited number of 

 organic substances, while the more important of the constit- 



