The Cellular Basis of Growth 39 



no correlation between age of plant and vein-islet area (and thus cell 



size). 



Even growth habit may involve differences in cell size, for H. B. Smith 

 ( 1927 ) reports that annual sweet clover has considerably larger cells than 

 does the biennial race. 



Correlation (p. 95), a sufficiently vague term to describe certain phe- 

 nomena about which we understand little, also affects cell size. In various 

 growth compensations, removal of an organ results in greater growth of 

 another one and often in larger cells there. In "topped" tobacco plants 

 (where the terminal flower cluster has been removed) Avery (1934) 

 found that the leaves on the upper third of the stalk grew larger and that 

 much of this extra growth was due to increase in cell size (Fig. 3-11). 

 Lindemuth (1904) removed and rooted mature begonia leaves and ob- 



Fig. 3-11. Effect of topping a tobacco plant. Portion of the vein network in the 

 twentieth leaf from the tip. At left, untopped; at right, topped. The leaves from topped 

 plants are larger and have more space between the veins because of increased cell 

 size. ( From Avery. ) 



served that they then increased considerably in size, chiefly because of 

 cell enlargement. While they were attached to the plant this presumably 

 was prevented by "correlative inhibition." Similar results have been re- 

 ported by others. In linden leaves, however, which had been induced to 

 grow much larger than their normal size by the removal of other leaves, 

 Ewart ( 1906 ) found the increase to be due chiefly to a larger number 

 of cells. 



Factors within the cell itself are doubtless related to the onset of its 

 division. Cytoplasmic viscosity generally rises in prophase, falls in meta- 

 phase, and rises again in telophase. Mole-Bajer ( 1953 ) has explored the 

 effect of artificially increased viscosity of cytoplasm in slowing down the 

 rate of mitotic division. Gustafsson ( 1939 ) found that the difference 

 between meiotic and mitotic division was related to the degree of hydra- 



