462 Comparative Physiology. 



undergo various modifications and transformations by whicli 

 they are converted into the elementary organic tissues." At 

 p. 1437. he describes buds as being the result of superfluous 

 ma,tter, separated in an undeveloped state of organisation from 

 the system, the special organisation of the system being subse- 

 quently developed by its connexion. When we see sap, extra- 

 vasatecl on parts of plants that have been cut accidentally, formed 

 into masses of buds from its connexion merely with the living 

 tissue, it must strike us that here at least is an accidental form- 

 ation that could not have been contained in embryo in the 

 germ, and that the doctrine is at least too far stretched when 

 it is maintained that all the parts ever to be developed are con- 

 tained in the germ. So well is tins fact known to gardeners, 

 that they are in the habit of cutting notches in bare stems to 

 produce buds from the extravasation of sap, when they wish 

 to clothe the stem with shoots without cutting in the head. 

 The activity of the living princij)le varies much in the diflerent 

 species of living beings ; it varies also in different individuals of 

 the same species, and at different periods in the same individual ; 

 and it is not from the quantity of aliment introduced into the 

 stomach of the animal, or into the soil the stomach of the plant, 

 that we can correspondingly produce growth. Much depends 

 on the activity of the absorbent vessels, and on the activity of 

 the assimilating organs after being absorbed. It arises from 

 this that a check given to growth in young seedling crops is per- 

 manently injurious and should be guarded against, and that if 

 we can by any means, as cutting in the shoots of young plants, 

 give accelerated activity to the vital principle, it is likely to 

 continue, if fostered. Aliment is essential, and growth cannot 

 be carried on without it, but other things must be attended to 

 besides merely exhibiting food. By keeping the soil open 

 and porous we increase heat, introduce air, and facilitate the 

 healthy action of the stomach of plants. 



" The supply of aliment is required not only to develope the 

 organism, but for its maintenance also. The tendency to de- 

 compose exists not only in dead organic matter, but in the 

 living tissues ; and, as already stated, it is probable the peculiar 

 influence of vitality is exercised not so much in resisting that 

 tendency as in providing for its effects by the removal of all 

 particles in a state of incipient decay: the supply of new ali- 

 mentary materials must be equal in quantity and regularity. 

 This may be regarded as the principal source of the continued 

 demand for nutriment in the adult system. The regeneration 

 of organs and tissues, after what appeared their total destruction 

 by disease or accident, is a process no less remarkable than their 

 first formation, and no less evidently displays the foresight of 

 the original Designer. In the harder parts of animals and vege- 



