BOTANICAL BIOLOGY. 415 



cesses by which the insoliiblo starch is made available for nutrition are, 

 1 can not doubt, closely similar in either case. 



When we inquire further about these mysterious and all-important 

 bodies, the answer we can give is extremely inadequate. It is very 

 difficult to obtain them in amount sufficient for analysis, or in a state 

 of purity. We know however that they are closely allied to albumi- 

 noids, and contain nitrogen in varying proportion. Papain, which is a 

 vegetable ferment derived from the fruit of the papaw, and capable of 

 digesting most animal albuminoids, is said to have the same ultimate 

 com})osition as the pancreatic ferment and as peptones, bodies closely 

 allied to proteids 5 the properties of all three bodies are however very 

 different. It seems clear nevertheless that ferments must be closely 

 allied to proteids, and like these bodies, they are no doubt directly 

 derived from protoplasnu 



I need not remind you that, unlike other constituents of plant tissues, 

 protoplasm, as a condition of its vitality, is in a constant state of molec- 

 ular activity. The maintenance of this activity involves the supply of 

 energy, and this is partly derived frouj the waste of its own substance. 

 This "self-decomposition" of the protoplasm liberates energy, and in 

 doing so gives rise to a number of more stable bodies than protoplasm. 

 Some of these are used up again in nutrition ; others are thrown aside, 

 and are never drawn again into the inner circle of vital processes. In 

 the animal organism, where the strictest economy of bulk is a paramount 

 necessity, they are promptly got rid of by the process of excretion. In 

 the vegetable economy these residual products usually remain. And it is 

 for this reason, I may pointout, that the study of the chemistry of plant 

 nutrition appears to me of such, immense importance. The record of 

 chemical change is so much more carefull.y preserved ; and the proba- 

 bility of our being able to trace the course it has followed is conse- 

 quently far more likely to be attended with success. 



This i)reservation in the plant of the residual by-products of proto- 

 plasmic activity no doubt accounts for the circumstance which otherwise 

 is extremely perplexing, — the profusion of substances which we meet 

 with in the vegetable kingdom to which it is hard to attribute any use- 

 ful purpose. It seems probable that ferments, in a great many cases, 

 belong to the same category. I imagine that it is in some degree acci- 

 dental that some of them liave been mad(5 use of, and thus the plant 

 has been able to temi)orarily lock up accumulaitons of food to l)e 

 drawn upon in future phases of its life with the certainty that they 

 would be available. Without the ferments, the key of the storehouse 

 would be lost irretrievably. 



Plants moreover are now known to possess ferments, and the luim- 

 ber will doubtless increase, to which it is difficult to attribute any use- 

 ful function. I'apain, to which I have already alluded, abounds in the 

 papaw, but it is not easy to assign to it any definite function ; still less 

 is it easy, on teleological grounds, to account for the rennet ferment 



