OF FORCE. 197 



It is diflicull to determine the influence of light on vegetables : it has been considered 

 that its influence was necessary to fix carbon ; or in other words, change Xhe crude sap and 

 render it fit for the nourishment of tlie plant. Potatoes and many other bodies receive ac- 

 cessions of matter, though always beneath the surface and excluded from light, and yet in 

 all bodies of this kind light is necessary; yet starch is formed in tubers and subterranean 

 stems ; it is not carried there already formed by the sap, it is a substance formed in the 

 place where we find it, and by a force residing in the cells of the root or stem itself. Ac- 

 cession of matter may be made to growing bodies in darkness as well as in light ; pumpkin 

 vines increase in length rapidly in the night. The previous stimulus of light is probably 

 necessary to these results. 



We recognize in the forces which have been spoken of external and internal forces. 

 Light and heat are external, and it is remarkable that vernal and autumnal heat and light 

 produce modified results. Heat begins to decline in intensity by the middle of August, as 

 may be observed by consulting the table of temperature recorded in the second volume. 



Mulder takes the ground that force can not be transferred from one being to another — 

 from the parent to the offspring. If this view is admitted, says the same distinguished 

 chemist, then the transmitted force is lost to themselves. This idea of Mulder's seems 

 too mechanical ; and indeed why is it not true that force is lost 1 Trees which bear heavy 

 crops will bear usually only on alternate years. The peach is supposed by Downing to be 

 enfeebled by allowing it to ripen a burden of fruit, the ultimate consequence of which is, 

 that it is attacked with the yellows, and is irrecoverably lost. What is called vital force 

 is here expended, and expended in the ripening of seed. Trees in a state of nature never 

 produce excessive crops, and rarely, if ever, exhibit a premature decay, and yet it will be 

 observed that they have their bearing years ; but the cultivated trees do exhibit the effects 

 of excessive bearing, in a premature decay and death. But annual herbaceous plants, as 

 the poppy, produce multitudes of seed, and die, having as individuals performed their 

 functions. The position which Mulder assumes may be right, yet it seems to me that his 

 argument is wrong if we appeal to phenomena. Whether right or wrong, theoretically, it 

 is necessary to bear in mind that, in consequence of excessive bearing, trees become en- 

 feebled, and may soon perish from the induction of a chronic disease or from mere ex- 

 haustion. All intelligent pomologists agree upon this point, and point out the remedy, 

 which consists in removing the unripe fruit ; and it would appear that they suffer more 

 from the ripening process than in the early growth of the fruit. 



The production of a new being is only functional, and, like other functions, is liable to 

 derangements. Excessive action of the liver and kidney is followed by a state of compa- 

 rative inaction ; and there can be no doulH that the inaction is due to a loss of force. The 

 organ first suffers, and if it does not .soon recover the whole system is sure to suffer also. 

 But there is connected with production health as well as disease. Force should be exer- 

 cised, and it only remains for us to ascertain how much force can be expended, and yet 

 vigor or force preserve its strength unimpaired. Life is not shortened_by the use of the 

 organs ; all that is requisite is to prevent excessive functional action. 



