PLANT CELL GROWTH AND NUTRITION 473 



TABLE V 



Absorption of Cs^'^''' by Proliferating and Non -Pro h'f era ting 



Carrot- Tissue Cells, With and Without the Addition 



of Non-Radioactive Cessium 



Days after Inoculation 

 Tissue 4 7 10 14 



Rapidly growing cul- With 



tures, stimulated by co- carrier cesium 7.30 9.14 14.1 13.4 



conut milk, increasing Without 



in cell number carrier cesium 9.43 10.7 12.9 14.5 



Cultures 7iot stimulated With 



to grow by coconut carrier cesium 27.2 53.1 77.7 79.5 



milk: cells growing Without 



sluggishly and mainly carrier cesium 375 649 2050 2130 



by enlargement" 



" The entries for the slow-growing cells represent accumulation ratios of Cs''^'', 

 measured by the counts per second per gram of tissue (fresh weight) divided by 

 counts per second per cubic centimeter of the external solution. 



in which, because of a lack of the cell-division growth factors, the cells 

 tend to grow by enlargement rather than by cell division (see second 

 section of Table V). In these cells the degree of accumulation (as 

 measured by the accumulation ratio) is greatest from the most dilute 

 solutions; this is a common feature. Consequently the accumulation 

 from a fixed concentration of the radioactive ion is greatly reduced by 

 the presence of the inert carrier cesium. 



A striking, but nonetheless curious, example of these contrasting 

 behaviors of cells is illustrated by Figure 9, presenting experiments on 

 tissue from tubers of Jerusalem artichoke {Helianthus tiiberosus). Un- 

 like the situation in the case of potato tubers, the initially high respira- 

 tion (COo production) of freshly cut Jerusalem artichoke disks or ex- 

 plants in water declines sharply with time. After some eight days the 

 respiration rate has reached a much lower and somewhat constant level. 

 But in the presence of coconut milk the respiration rate is maintained 

 through this period at a considerably higher level. As in the case of the 

 carrot tissue, the more actively dividing tissue in a coconut milk medium 

 maintains a lower internal concentration of Cs^'^^, but absorption pro- 

 ceeds concomitantly with growth to maintain this level. By contrast, the 

 relatively non-proliferating tissue absorbs and stores Cs^^' in its ex- 

 panding cells and enlarging vacuoles, and the radiocesium reaches a 

 higher concentration in the tissue. If, after eight days, cell-division 



