476 PLANT GROWTH AND PLANT COMMUNITIES 



TABLE VI 



Effects of Radiation on Growth of Carrot Cultines by Cell Division 



and by Cell Enlargement" 



A. Effects of irradiation on growth induction by coconut milk 



Growth 



Period Not Irradiated Irradiated (0.10 X 16h) 



No. of cells Size of cells No. of cells Size of cells 

 per explant ' ( in micrograms per e.xplant (in micrograms 

 (in thousands) per cell) (in thousands) per cell) 



* The data in this table are taken from hitherto unpublished work with Dr. Z. I. 

 Kertesz of the New York State Geneva Agricultural E.xperiment Station and Cornell 

 University. 



growth by cell division. Simultaneously, the process of de novo protein 

 synthesis also is unleashed by the coconut milk stimulus, and Stage 1 

 of the process of ion intake, as described by Steward and Sutcliffe 

 ( 1959 ) , gets under way. To the extent that the radiated cells have a 

 residual ability to grow by cell enlargement, they ( and no doubt also 

 those treated with carbon monoxide and cyanide) can still absorb 

 some solutes into their vacuoles, but this is strictly limited unless con- 

 tinuous growth by cell division is restored. At this point one can only 

 say that the coconut milk stimulus which causes growth by cell division 

 may also cause some relatively drastic changes in the chromosome com- 

 plement, especially of free cells. This may be illustrated in a tissue 

 culture of Haplopoppus gracilis, studied by Dr. J. Mitra, working with 

 the author. In suitable combinations of coconut milk and either 2,4-D 

 or NAA, the stem tissue of this plant will grow, and its two pairs of 

 easily recognizable chromosomes (2n = 4) may now undergo easily 

 detectable changes. Thus the chemical stimulus administered by the 

 coconut milk, which induces the growth, is also exerted in the area in 

 which chromosome duplication (DNA) is taking place, and all the 



