The Cellular Basis of Growth 35 



Some "giant" races, however, owe their large size to larger cells. The 

 first instance of this was reported by Keeble (1912) in a mutant of 

 Primula sinensis. Tischler (1918) found a similar case in the reed Phrag- 

 mites communis, and here large cell size was accompanied by larger than 

 normal chromosome size, a fact reported by others ( Schwanitz and Pirson, 

 1955). Much more commonly, giant forms with large cells result from 

 polyploidy ( p. 436 ) . The first case of this to be observed was Oenothera 

 gigas of de Vries, which was found to be a tetraploid. Many similar ex- 

 amples are now known. Tetraploids are not always giant in character, 

 however, and many polyploid series in nature show no difference in body 

 size or cell size. Sinnott and Franklin ( 1943 ) found that in young tetra- 

 ploid gourd fruits the gigas condition, both as to ovary and cells, is pres- 

 ent until after flowering but that later growth is reduced so that at matu- 

 rity there are no great size differences between diploid and tetraploid (p. 

 439). A diploid giant moss race reported by von Wettstein (p. 437) 

 returned to normal size of cell and organ after a few years of vegetative 

 propagation. 



The increased cell size due to polyploidy is not uniform but is consid- 

 erably greater in some tissues than in others. In the diploid moss races 

 produced by von Wettstein ( 1924 ) the ratio of size increase from the In 

 to the 2nwas found to be characteristic for each race (p. 437). In general, 

 the increase of organ size due to polyploidy is not as great as the increase 

 in cell size, since cell number tends to be somewhat reduced. 



Increased cell size may also result from increased number or bulk of 

 chromosomes (p. 445), quite apart from polyploidy (Navashin, 1931; Lor- 

 beer, 1930), and from extra or accessory chromosomes (Randolph, 1941; 

 Miintzing and Akdik, 1948). Particular chromosomes, when present in 

 trisomies, have different effects on cell size (and on other characters), 

 presumably because of the specific genes which they contain (p. 447). 

 Geitler ( 1940 ) observed that chromosome volume was correlated with 

 nuclear volume and that in some tissues the chromosomes were more than 

 four times as large as in others. In species of four genera, Mrs. Sax ( 1938 ) 

 found that cell size was correlated with the chromosome number of the 

 species but that in three others there was no such correlation. Somatic 

 polyploidy or polysomaty ( p. 441 ) is a factor of importance both for cell 

 size and for differentiation. 



Cell size has been found to be inherited in a number of lower plants, 

 as in yeast (Townsend and Lindegren, 1954). 



Heterosis is usually not related to an increase in cell size (Kostoff and 

 Arutiunova, 1936). 



Cell Size and Position. Many workers have found a great variation in 

 size among comparable cells in the same plant. Often this is not ran- 

 dom but follows a certain pattern. The problem has been studied most 



