AGRICUI.TURAI, BOTANY, CHEMISTRY AND PHYSIOI^OGY OF PI^ANTS 1 26 1 



ternal conditions. He was able to find 20 pairs of vines answering to these 

 conditions, each pair consisting of a young and old vine. From each vine 

 he took 10 healthy, normal leaves which had reached full development, and 

 he examined the venation of these leaves. In this examination he took into 

 account the following principles previously established either by other ob- 

 servers or himself : the islets, bounded by ribs, are of a constant size in the 

 different parts of the leaf ; they are of the same size in leaves of different size 

 or thickness taken from one and the same plant ; furthermore, in leaves of 

 one and the same vine having a different solar exposure, the exposure has 

 no influence on the surface of the islets. 



In vines of different ages, however, the surface of the islets varies great- 

 ly, being much larger in the youngest vines : the variation ranges from 

 0.5154 sq. mm. in a 3 year old vine to 0.1376 sq. mm. in a 70 year old vine. 

 This dift'erence cannot be attributed to an5rthing but old age, the effect of 

 which is to give rise to a denser growth of the vein system, with a reduction 

 of the islets bounded by the ribs. From this a method is deduced for de- 

 termining the age of Vitis vidpina by mere examination of the venation and 

 the following table is given for that purpose : 



He verified the conclusions to which he had been led from examina- 

 tion of the leaves of V. vulpina b}^ checking with other plants : Vitis bico- 

 lor, IvC Conte, Tecoma radicans L., Salix nigra March, Castanea dent at a Bork, 

 Qiiercus alba L., Tilia americana L., Ulimis americana h-, Carya alba Koch, 

 Carya ovata Koch, Acer saccharinitm ly., Acer saccharum Marsh, Quercus 

 velutina Lam., Platanus occidentalis L,., and Fraxinns americana ly. These 

 plants aU allowed of the same observations as to the influence of age with 

 regard to the venation. 



If age affects the meristematic tissues of seed-producing plants, the 

 cells of the scions used for propagating certain varieties must be equally 

 affected. The writer having considered this hypothesis verified it by his 

 observations : plants produced by grafting are, as regards the leaves, of 

 the age of the plant which furnished the scion, this age being reckoned 

 from the time of production of the parent plant from seed ; grafting and 

 growth on the host do not renovate the youth of the tissues of the scion. 



These conclusions are next discussed, and the causes to which the seni- 

 lity of leaves is to be attributed are sought for. The insufficiency of convey- 

 ance of nutrient Hquids by the vessels of plants which have grown old is 

 dismissed. The possibility of the production of toxins is an attractive 

 hypothesis, but there is no direct and evident proof of their existence, and 

 this hypothesis must be abandoned, because senility persists in cuttings 

 separated from the old plant. It is therefore suggested that the visible 



