AGRICULTURAL BOTANY, CHEMISTRY AND PHYSIOIvOGY OF PLANTS I263 



Average longitudinal diameter of the siomata. 



Vines from 5 to 7 years 16.6 [X 



Vine from 20 to 30 years 10.8 [X 



Similar results were also obtained by the measurement of the cells of 

 the palisade layer in the leaves (12.2 [i in the 5 year old vines as against 

 10.3 fjt in those of 20 year old vines) and by determining the ratio between 

 the cytoplasm and the nucleus (this ratio being 388 to i in the vines aged 

 from 5 to 7 years, as against 478 to i in those of 20 to 30 years) ; neverthe- 

 less this latter determination does not present all the necessary conditions 

 of accuracy. 



The writer next draws conclusions from these observations, and in 

 particular envisages their application to the question of the degeneration 

 of plants reproduced by scions or slips ; he lays stress on the interest at- 

 taching to investigations on this important question. Finally he examines 

 and generalises the theories of senilit}', in order to extend them both to 

 the animal and vegetable kingdom. He rejects the theories relating to the 

 localisation of senile modifications, including the theory of Metchnikoff 

 on the part played b}^ toxins secreted in the main intestine of animals and 

 in the flower of plants. He likewise does not admit that old age is due to 

 the accumulation of katabolic products, or to the decreasing ehmination 

 from the body of the products of secretion of cells placed far away from the 

 surface. To him, old age results from a physical or chemical degeneration 

 involving the protoplasm itself, producing among other changes a diminu- 

 tion of permeability, and he concludes that the evidence appears very 

 strong, both from the point of view of senility and that of regeneration, 

 that the duration of life is directly bound up with the degree of permeability 

 found in that part of the living cell which is in contact with the surrounding 

 universe, and that in proportion as the activities of life continue, the 

 cell is entombed by an inexorable diminution in the permeability of its pro- 

 toplasm. The fundamental cause of this diminution may very well be the 

 colloidal nature of protoplasm. The relatively simple relations existing 

 in non-living complex colloidal bodies tend to be modified under the action 

 of external forces, or even by the mere action of time ; it seems inevitable 

 that the extremely complex colloidal states which form protoplasm should 

 be modified progressively by the activities of life and by the intervention 

 of external forces. What should give rise to astonishnient is not the senile 

 modifications of the protoplasm, but their tardiness in appearing. 



Regeneration is the process by which the original arrangement of the 

 colloidal elements constituting the protoplasmic colloids is restored. 



Sexual reproduction is one of the methods by which this regeneration 

 is accomplished, while it is ensured by more primitive methods in asexual 

 plants. 



It is for the future to solve the question whether the progress of seni- 

 lity in sexed plants and animals can be arrested or even retarded b}^ means 

 of regeneration such as are utilised in asexual forms, and which are thus 

 to a certain extent applicable to the whole of the somatic cells. The know- 



