Senile Changes in Leaves op Certain Plants 



313 



various vines studied. These cuttings were grown in water and in soil 

 cultures, and the leaves that developed were measured and studied. 

 The cuttings were classified into groups according to the age of the vine 

 from which they were taken, and were labeled accordingly but grown 

 together under identical conditions. 



Of the first series of cuttings grown in tap water, seventeen proved 

 successful. They were grown in a greenhouse at Ithaca. Since it was 

 necessary for the writer to go to Cincinnati at the close of the summer, 

 the measurements of the vein islets were made before the leaves had 

 attained maturity. The results of these measurements are given in 

 table 23. The number of rings as given in the table indicates the age of 

 the vine from which the cuttings were made; the size given for the vein 

 islets is the average for all the leaves of one cutting. 



TABLE 23. Area of Vein Islets in Leaves from Cuttings Grown in Tap Water 





« 



Number o 



rings 







4 to 5 



7 to 11 



14 to 16 



25 to 50 





(Square 

 millimeters) 

 0.24 

 0.26 

 0.29 

 0.30 



(Square 

 millimeters) 

 0.20 

 0.21 

 0.22 

 0.23 

 0.32 



( Square 

 millimeters) 

 0.16 

 0.22 

 0.17 

 0.18 



(Square 

 millimeters) 

 0.14 

 0.15 

 15 

 0,15 



Average 



0.27 



0.24 



0.18 



0.15 



The vein islets are noticeably smaller than those in leaves grown under 

 natural conditions, and this is due to the fact that the leaves were not 

 fully expanded. The smaller the leaf, the smaller are the islets until 

 the maturity of the leaf is reached. These differences in size of vein 

 islets of leaves of old and of young vines are obvious at the time when 

 the leaf buds first open, and are maintained throughout the later stages 

 of leaf growth, as is shown by tables 24 and 25, pages 314 and 315. 



