344 



Hareis M. Benedict 



COMPARISON OF SIZES OF PALISADE CELLS IN LEAVES OF YOUNG AND OF 

 OLD VINES OF VITIS VULPINA 



The cells of the palisade layer are much more regular in size and form 

 than any others in the leaf, and therefore best adapted for the determi- 

 nation of the effect of increasing age on the size of the cells of the leaf. 

 In table 58 the measurement given is the length of the cell measured 

 perpendicularly to the surface of the leaf, as seen in cross section. 



TABLE 58. 



Size of Cells of the Palisade Later of Leaves of Young and of Old 

 Cuttings of Vitis Vulpina 





For 3 vines 





For 3 Amines 





with 5 rings 





with 20 rings 





(microns) 





(microns) 





'14.6 





11.0 





11.9 





11.0 





11.9 





11.0 





11.9 





9.0 





12.8 





11.0 





11.9 





14.6 





12.1 





10.0 





11.9 





11.0 





11.0 





9.0 





12.0 





• 9.0 





11.0 





9.0 





14.6 





9.0 





11.0 



Average. . . . 



9.0 



Average .... 



12.2 



10.3 



The cells of the pahsade layer thus show a distinct decrease in size 

 even in the leaves of the plants twenty years old, w^hich are in their vigor- 

 ous maturity. The guard cells of the stomata, in the cases observed, also 

 show the same change in size with age. This change in size shown by 

 the two most regular cells of the leaf is seemingly apparent in all the pho- 

 tosynthetic cells as well. As regards the cells of the veinlets, this decrease 

 in size with age is doubtful and will require more study. It is possible 

 that the physiological stimulus which calls forth an increasing development 

 of vascular tissue in the older plants msiy likewise so stimulate the develop- 

 ment of the vascular cells as to neutralize, for a time, the tendency toward 

 a reduced size. Some evidence to this effect has been observed. 



These few observations indicate that possibly there is a difference 

 in number of stomata in the leaves of young and of old vines, together 



