DYNAMICS OF GERMINATION. 413 



living body, is unmistakably manifested. To some of those 

 phenomena, which afford the best illustrations of the mode 

 in which Heat acts upon the living organism, attention will 

 now be directed. 



Commencing with the Vegetable kingdom, we find that the 

 operation of Heat as the motive power or dynamical agency, 

 to which the phenomena of growth and development are to be 

 referred, is peculiarly well seen in the process of Germina- 

 tion. The seed consists of an embryo which has already ad- 

 vanced to a certain stage of development, and of a store of 

 nutriment laid up as the material for its further evolution ; 

 and in the fact that this evolution is carried on at the expense 

 of organic compounds already prepared by extrinsic agency, 

 until (the store of these being exhausted) the young plant is 

 sufficiently far advanced in its development to be able to elab- 

 orate them for itself, the condition of the germinating embryo 

 resembles that of an Animal. Now, the seed may remain 

 (under favourable circumstances) in a state of absolute inac- 

 tion during an unlimited period. If secluded from the free 

 access of air and moisture, and kept at a low temperature, it 

 is removed from all influences that would on the one hand 

 occasion its disintegration, or on the other, would call it into 

 active life. But when again exposed to air and moisture, and 

 subjected to a higher temperature, it either germinates or de- 

 cays, according as the embryo it contains has or has not pre- 

 served its vital endowments a question which only experi- 

 ment can resolve. The process of germination is by no means 

 a simple one. The nutriment stored up in the seed is in great 

 part in the condition of insoluble starch ; and this must be 

 brought into a soluble form before it can be appropriated by 

 the embryo. The metamorphosis is effected by the agency of 

 a ferment termed diastase, which is laid up in the immediate 

 neighbourhood of the embryo, and which, when brought to 

 act on starch, converts it in the first instance into soluble dex- 

 trine, and then (if its action be continued) into sugar. The 



