DECLINE OF PLANTS. 



approach of old age. The tubers of the potato continue to diminish in quantity; they now 

 also lose their quality, till the plant becomes utterly useless. So the branches of the de- 

 clining tree become gradually more meagre, and fruit is sparingly, and less frequently 

 produced; thereby indicating that in the branches of the aged tree, as well as in the tu- 

 bers of the aged potato plant, there must Vje a progressive diminution in the quantity of 

 the secretions deposited. How admirably this conclusion is borne out by an observation 

 by Mr. Knight; "the wood of all the old fruit trees," said he, " has long appeared to 

 me to possess less elasticity and hardness, and to feel more soft and spongy under the 

 the knife, than that of new varieties. This defect may, I think, be the immediate cause 

 of the canker and moss, though it is probably, itself, the effect of old age, and therefore 

 incurable." 



If I may hazard an opinion as to the cause of these progressive changes, I would sug- 

 gest whether they are not simply owing to a progressive diminution in the activity of the 

 absorbent vessels. We see that the vigor of the growth of a tree, and of a varietj' of po- 

 tato, is in proportion to their youth ; may not, therefore, the rapidity of the circulation 

 of the fluids, as well as their abundance, dimini.sh as the tree or potato becomes aged. If 

 there is more energetic absorption by the roots in youth, may not the sap be propelled 

 with greater force, under ordinary circumstances, than in mature, or old age, and thus 

 circulate with greater rapidity, through the leaves; therefore be less elaborated, retain 

 more of a fluid character, and be unsuited for the formation of blossom buds, or the sup- 

 port of fruit, though admirably adapted for the formation of fresh branches and roots. 

 May not, also, the gradual diminution of the growth of branches and tubers, and the cor- 

 responding increase of the density of secretions, as the tree or potato approaches the prime 

 of life, be owing to a more moderate yet more liberal supply, and to a less rapid flow of 

 the sap; in consequence of which it passes more deliberately through the leaves, becomes 

 more highly elaborated, and therefore better suited to the production of blossoms and 

 fruit, than in its youth. 



The increase of the roots of a tree is commensurate with the increase of its branches ; 

 if we head-back the branches of a healthy tree in full bearing, it immediately produces 

 strong, sappy shoots, because the absorbent power of the roots is equivalent to the wants 

 of a greater breadth of foliage, and little or no fruit is produced till the balance between 

 ■ branches and roots is nearly restored. Thus a similar effect is produced, as by the small- 

 er system of roots, but more energetic absorbent power of a tree newly raised from seed. 

 If, on the other hand, we allow the branches of a vigorous tree to remain, and adopt 

 means to diminish its roots, as by the practice of root-pruning, we diminish the supply of 

 sap, diminish the growth of branches, and make the tree more fruitful. 



I desire further to suggest, whether it is not probable, that not only must there be a 

 progressive diminution in the absorbent power of a plant as it becomes aged, but whether 

 its annual efforts must not be less sustained in age, than in youth. Early in the season 

 tissue is most rapidly developed; as the season advances it is perfected, or solidified. Ac- 

 cording to the brightness of the light, or as the season is favorable to the exertions of the 

 plant, all other circumstances being similar, so is the density of its secretions, or the 

 amount of matter which it is capable of depositing in previously formed cells. Now, do 

 not the soft spongy tubers of a nearly expended variety of the potato, and the spongy 

 branches, and irregularly ripened fruit of an aged tree, indicate that the exertions of the 

 plant must become so feeble as autumn approaches, that it is not able to absorb and ela 

 borate a sufficient quantity of sap to perfect the tissue, or feed the whole of the fruit 

 it formed in spring. 



