208 2>r. Carpenter, on the Relation [Feb. 24, 



power that does the work. It has been from the narrow limitation of 

 the area over which physiological research has been commonly pro- 

 secuted, that the intimacy of this relationship between heat and the 

 organizing force has not sooner become apparent. Whilst the vital 

 phenomena of warm-blooded animals, which possess within themselves 

 the means of maintaining a constant temperature, were made the sole, 

 or at any rate the chief objects of study, it was not likely that the 

 inquirer would recognize the influence of external heat in accelerating, 

 or of cold in retarding, their functional activity. It is only when the 

 survey is extended to cold-blooded animals and to plants, that the 

 immediate and direct relation between Heat and Vital energy, as 

 manifested in the rate of growth and development, or of other changes 

 peculiar to the living body, is unmistakeably manifested. 



The action of Heat on the Vegetable kingdom, it is true, cannot be 

 fully effective without Light ; but this latter force would appear to be 

 concerned rather in providing the materials at the expense of which 

 the plant grows, than in converting these materials into living tissue. 

 Its action is limited to the surface ; and it is mainly exerted in decom- 

 posing the carbonic acid of the surrounding medium, and in uniting the 

 carbon, (oxygen being set free) with oxygen and hydrogen, to form 

 starch, chlorophyll, &c., and with nitrogen in addition to form albu- 

 minous compounds-. If supplied with these by other means, plants can 

 grow without light ; as we see in the instances of the germinating seed, 

 which lives on the store laid up by its parent in the cotyledons, and of 

 leafless parasites and fungi, which appropriate materials previously pre- 

 pared by other plants. On the other hand, the rate at which germina- 

 tion proceeds is entirely regulated by the degree of heat to which the 

 seed is subjected ; and the same thing is true with regard to the rate of 

 development of the egg in cold-blooded animals. By the time that the 

 plumula of the young plant is beginning to unfold, the store of material 

 laid up in the seed is exhausted ; and henceforth the plant is mainly 

 dependent upon Light for the power of forming (at the expense of the 

 materials supplied by the inorganic world) those organic compounds, 

 without a due supply of which no further growth or development can 

 take place ; the continued action of Heat being required to turn these 

 materials to account. 



A note-worthy suggestion has lately been made by Prof. Le Conte 

 (of South Carolina College, U.S.), with reference to the fact that in 

 germination a certain proportion of these organic compounds is given 

 back to the inorganic world, in that liberation of carbonic acid which 

 is a remarkable feature of the process ; and that, during the whole sub- 

 sequent life of plants, a similar process is continually taking place to 

 a certain extent, even whilst the green surfaces of the plant are most 

 actively engaged in fixing carbon from the atmosphere, and in generat- 

 ing organic compounds. May not the force liberated (he asks) in the fall 

 of a certain portion of these organic products down to the lower level of 

 simple binary compounds, be necessary for the elevation of another 

 portion to the rank of living tissue ? That such is not unlikely to be 



