91 



ness. Consequently, instead of attempting to find the relation- 

 ship between the volume of the nucleus and cytoplasm, an 

 attempt was made to find the relationship between the volume 

 of the nucleus and that of the entire cell — the cytoniiclear rela- 

 tionship in plant cells. 



The method of approach has been a simple one. Camera 

 lucida drawings of cells and nuclei were made, the drawings 

 measured and volumes determined. Stem and root tip meristems 

 of a number of representative families of the higher plants 

 were used, leaves of the aquatic plant Elodea, and stem hairs 

 of tomato plants. In ordinary meristem tissue, nuclear volume 

 bears a definite relationship to cell volume, large cells having 

 larger nuclei than small cells, but as cell size increases, nuclear 

 size does not increase as fast. The relative rates of change, how- 

 ever, are constant, so that when plotted logarithmically, a 

 straight line results. The fact that the slope of the line is about 

 .67 indicates that the nucleus is growing only about two-thirds 

 as rapidly as the cell, and as a result, the volume of the nucleus 

 is keeping pace with the surface of the cell (the surface of a 

 sphere growing as the square of its linear dimensions and the 

 volume as their cube, as a result of which the surface of a 

 spherical cell will increase two-thirds as fast as its volume). 

 The relationship holds for experimentally enlarged nuclei — in 

 polyploid cells of the root tip induced by colchicine treatment. 

 Further studies were undertaken to discover whether any 

 change occurs in the cytonuclear ratio during the growth 

 phases of elongation and differentiation. The relationship ap- 

 parently is maintained throughout development in the onion 

 root tip for cells of different sizes at the same stage of develop- 

 ment, but final cell size may be as much as one hundred times, 

 and nuclear size three times greater than meristematic size. 

 Stem tip material offers three distinct developmental types — 

 one, similar to the developing onion root tip; a second, one in 

 which nuclear size remains the same in the meristem, but in- 

 creases when meristematic activity stops; and a third, one in 

 which the relationship of cell to nucleus found in the meristem, 

 is maintained throughout development. The method of ap- 

 proach in this study — the method of heterogonic growth pro- 

 posed by Huxley — is rather significant here. 



Clyde Ch.\ndler 

 Recording Secretary 



