414 CORRELATION OF PHYSICAL AND VITAL FORCES. 



dextrine and sugar, combined with the albuminous and oily 

 compounds also stored up in the seed, form the "protoplasm," 

 which is the substance immediately supplied to the young 

 plant as the material of its tissues ; and the conversion of this 

 protoplasm into various forms of organized tissue, which be- 

 come more and more differentiated as development advances, 

 is obviously referable to the vital activity of the germ. Now 

 it can be very easily shown experimentally that the rate of 

 growth in the germinating embryo is so closely related (within 

 certain limits) to the amount of heat supplied, as to place its 

 dependence on that agency beyond reasonable question : so 

 that we seem fully entitled to say that Heat, acting through 

 the germ, supplies the constructive force or power by which the 

 Vegetable fabric is built up.* But there appears to be another 

 source of that power in the seed itself. In the conversion of 

 the insoluble starch of the seed into sugar, and probably also 

 in a further metamorphosis of a part of that sugar, a large 

 quantity of carbon is eliminate'd from the seed by combining 

 with the oxygen of the air, so as to form carbonic acid ; this 

 combination is necessarily attended with a disengagement of 

 heat, which becomes very sensible when (as in molting) a 

 large number of germinating seeds are aggregated together ; 

 and it cannot but be regarded as probable that the heat thus 

 evolved within the seed concurs with that derived from with- 

 out, in supplying to the germ the force that promotes its evo- 

 lution. 



* The effect of Heat is doubtless manifested very differently by differ- 

 ent seeds ; such variations being partly specific, partly individual. But 

 these are no greater than we see in the inorganic world : the increment of 

 temperature and the augmentation of bulk exhibited by different substances 

 when subjected to the same absolute measure of heat, being as diverse as 

 the substances themselves. The whole process of " Malting," it may be 

 remarked, is based on the regularity with which the seeds of a particular 

 species may be at any time forced to a definite rate of germination by a 

 definite increment of temperature. 



