328 Harris M. Benedict 



under natural conditions, the evident luxuriance of growth and the health- 

 ful appearance of the leaves does not suggest the presence of toxins. 

 Any toxin that would act solely on the venation of the leaf could do so 

 only through mechanical obstruction of the vessels. Since any toxins 

 that reach the leaves must be soluble and readily diffusible through 

 protoplasm, such obstructive action is hardly possible. 



The fact that the removal of cuttings from contact with the old vine 

 and their subsequent growth on their own newly developed roots did not 

 cause a distinct increase in size of the vein islets in their leaves, is a con- 

 vincing demonstration of the inadequacy of the toxin theory. If leaves 

 removed from contact with a suspected source of toxins show the same 

 characters as those that remain in contact with it, then the absence of the 

 suspected toxins is established. The possibiHty that a permanent poison- 

 ing may have been produced in the twig before it was removed from the 

 vine as a cutting, is opposed to the universal recuperative power that all 

 life possesses. The growth of cuttings on their own roots or on the roots of 

 seedlings estabhshes the conditions needed for complete recuperation from 

 the effect of any toxin so feeble as to cause no evident decrease in the vigor 

 of growth, even when contact with continuous contamination is unbroken. 

 The cuttings of large diameter which had several annual rings and had 

 therefore been subjected to any possible toxic action three times as long 

 as had cuttings from the same vine with one ring, produced leaves whose 

 vein islets were of the same size as those in the smaller cuttings. 



The idea may be dismissed, therefore, that conduction of toxic products 

 from the stem into the leaves is the primarj^ cause of the decrease in size 

 of vein islets that comes with age. It may be true that there is later some 

 effect of this kind, but it cannot be considered the primary cause. Of 

 course, when the trunk is decajdng or is suffering from the attacks of other 

 organisms, the toxins produced are the results of external agencies and the 

 case is one of disease, not seniHty. Even in such striking cases as those 

 in which great hollows are formed by the decay of the heartwood, the 

 leaves often seem to be suffering no toxic action. 



It is possible that one of the accompaniments of senility is an increase 

 of toxic products in the cells. But if such were the case, this accumulation 

 would not be confined to any one class of cells, but would occur in all 

 cells of the senile organism. The cells of the leaf would suffer from their 

 own toxic products as the plant becomes senile, and so would the other 



