198 



" Mr. Beuedict's interesting and valuable investigations on, 

 tJio senile decay and loss of fruitfiilness in plants contained material 

 ot special interest to fruit growers. N"ot the least interesting part 

 of the i^aper is that in which he appeals to the opinion of that 

 remarkable English horticulturist Thomas Andrew Knight, who. 

 upwards of a century ago (KOo) was occupied with this same 

 pr(>l)leni of senility of plants. Knight in fact, came, as the result 

 of his experiments with Apples and Pears, to the same conclusion 

 as that reached by Mr. Benedict, and attributed to senility the 

 gradual failure of different varieties of fruit trees. He found in 

 liis grafting experiments that the vigour of grafts was influenced 

 ))y the age of the tree from which they were taken, and with the 

 acumen of genius he appealed in support of his opinion to the 

 common phenomena presented by certain woodland trees. He ob- 

 serves tliat certain of them, such as the Aspen, send up multitudes 

 of root-suckers, and adds " were a tree capable of affording an in- 

 ternal succession of healthy plants from its roots, I think our 

 woods must have been wholly over-run with those species of trees 

 which propagate in this manner, as these scions from the roots 

 always gTow in the hrst three or four years with much greater 

 rapidity than seedling plants. 



"In another paper published in 1810 and entitled "On the 

 Parts of Trees Primarily Impaired by Age." Knight makes the 

 yet more remarkable comment : — " I am disposed to at- 

 tribute the disease and debility of old age in trees to an inability to 

 l)roduce leaves which can efficiently execute their natural office. 

 It is true that the leaves are naturally reproduced and therefore 

 annually new, but there is, I conceive, a very essential difference 

 between the new leaves of an old and of a young variety." This 

 difference after over a hundred years, would seem to have been now 

 demon stra tech 



"It may be added that j\lr. Benedict has extended his obser- 

 vations on the veining of young and old varieties, to fruits other 

 than the vine and he found in the case of Apples, Pears, Plums 

 and Peaches tluit increasing age is accompanied by the same con- 

 centration of small veins as occurs in the vine. Hence it would 

 seem that it might be possible to ascertain approximately tlie age 

 of a tree l)y an examination of one of its this year's leaves ! 



" Finally reference should Ije made to the interesting but purely 

 s[)eculative hyjjotheses of old age in plants which have teen ad- 

 vanced. ,0f tbese liypotheses that of Metchnikoff deserves mention. 

 It may be described as the "guilty organ" hypothesis, in that he 

 ascribes old age to the failure of one organ of the body : in the 

 human ])ody the large intestine is the sinner; in annual plants 

 Mctchiiikotf ascribes to the flower-head the guilt of producing toxins 

 (|)(iis(iii) which destroy the vegetable parts. 



'" Another hypothesis ascril)es senility to cell specialisation. On 

 tills an unspecialised cell is immortal, but a cell, the moment it 

 becomes a specialist at certain kinds of work puts off immortality 

 and becomes mortal ; but against this view is the fact tliat a 



