394 Cow-paratwe Physiology. 



to possess the nutritive function in a higher degree than mode- 

 rately fed ones that are more healthy. Precocity may be in- 

 duced by starvation, but not fertility. The reproductive func- 

 tion is undoubtedly antagonist to the nutritive, but it is also 

 dependent on it ; and fruitfulness is, perhaps, greatest in animals 

 when the nutritive function is at full maturity, and before 

 it declines. In plants the contrary would appear to be the 

 case, as unhealthy stunted plants are most precocious. In 

 such, however, the function is never performed with the same 

 vigour, nor are the seedling plants from these ever so healthy 

 and strong.* In annual plants, such as grain crops, the quantity 

 and quality of the seeds increase, generally, as the vigour of 

 the nutritive function is induced, though it may be carried to 

 excess there also ; yet in these there seems a period of maturity 

 similar to that in animals. In trees a cessation of the vigour of 

 the nutritive function does indeed seem necessary to produce 

 reproduction : it is not till the tree has extended itself, and 

 until, by the slowness of the more impeded circulation, shorter 

 and less vigorous branches are produced, that the period of fruit- 

 fulness commences. This period may be hastened also by 

 starving the tree, and may be protracted by over-feeding ; as in 

 animals, so also in plants, plethora may be produced and death. 

 Plants, however, differ from animals in being a congregation of in- 

 dividual buds, each of which is capable of maintaining a separate 

 existence, and, under certain circumstances, of becoming seed. 

 The most essential of these circumstances seems to be, the quality 

 of the food : to produce that quality the elaboration of the leaf is 

 necessary ; and, to produce the necessary elaboration, the stimu- 

 lating and chemical power of the sunbeam is essential. Were 

 we able to produce the latter at will, we would not be so apt to 

 err in giving too miich food ; but, as it is not at our command, 

 we are necessitated to produce the necessary quality of the 

 food, by providing a smaller quantity to be elaborated. It is 

 well known to practical men that this is the case. Most of our 

 vegetable physiologists, however, contend that it is the quan- 

 tity of nourishment that produces fruitfulness. Mr. Knight 

 took this view of the subject. It is well known that taking a 

 ring of bai*k from the branch of a fruit tree induces fruit- 

 fulness in that branch, and this would seem to be brought 

 about by the less quantity of sap furnished to the branch. Mr. 

 Knight, however, supposed it to be owing to the accumulation 

 of the descending sap at the upper lip of the ring, as he found 

 the wood always of more specific gravity above than below the 



* Too little attention has been paid to this. Were the seeds of trees col- 

 lected only from vigorous young plants in place of stunted ones, which have 

 niost seed, the young trees would be found to have a more vigorous habit, 

 and produce more wood. 



