Senile Changes in Leaves of Certain Plants 345 



with changes in guard cells and palisade cells. The results are not con- 

 clusive enough to permit of definite conclusions, and the inadequacy 

 of the evidence does not warrant any explanation of its significance. 

 Suffice it to say that an increased number of stomata with smaller aper- 

 tures, while not permitting greater diffusion of carbon dioxide or oxygen 

 than the stomata of young leaves, would be a benefit to the plant in bring- 

 ing a larger area of palisade cells in closer proximity with air chambers. 

 If the permeability is decreased in the cells of leaves of old vines, then a 

 larger number of stomata per unit area would tend to counterbalance 

 the defect of decreased permeabihty. The stimulus to the production of 

 an increased number of stomata cannot be otherwise explained at the 

 present time. 



RELATIVE MASS OF NUCLEUS AND CYTOPLASM IN CELLS OF THE LEAF IN 

 YOUNG AND IN OLD VINES OF VITIS VULPINA 



• It will be remembered that the advance of senility in animal cells is 

 marked by a decrease in the relative amount of nuclear material as com- 

 pared with the amount of cytoplasm. Difficulty was experienced in making 

 such a comparison in the cells of the leaf, because of individual differ- 

 ences in the sizes of the nuclei of adjacent cells. The rapidity with which 

 a cell is working is indicated usually by temporary changes in the size 

 of its nucleus. The cells in the assimilating tissues of the leaf seemed to 

 be in different stages in each preparation, and the differences were great 

 enough to render doubtful the value of averages. The cells that did 

 show some uniformity in this respect were the border parenchyma cells 

 of the veinlets, and a series of measurements was made of these with tbe 

 following results: 



Proportion of cytoplasm to nucleus in vine with from 5 to 7 rings, 388 to 1 

 Proportion of cytoplasm to nucleus in vine with from 20 to 30 rings, 478 to 1 



The great difference in the lengths of these cells makes the calcula- 

 tions, even in the border parenchyma cells, unsatisfactory. This compar- 

 ison between nuclear and cytoplasmic material can probably be carried 

 out with greater accuracy on the meristematic tissue in the stem. In 

 the investigation of the effect of age on the tissues of the stem, which will 

 be the next phase of the problem attacked, a careful study of the propor- 

 tion of cytoplasm to nucleus wiU be made. 



