SURVIVAL OF ISOLATED TOMATO ROOTS AT SUBOPTIMAL AND SUPRAOPTIMAL TEMPERATURES

White's studies led in 1934 to the first prolonged cultivation of excised roots, in 1937 to development of satisfactory synthetic culture media, and in 1939 to prolonged cultivation of undifferentiated plant tissues.

“These studies led in 1934 to the first prolonged cultivation of excised roots (White, 1934, 65), to the development of satisfactory synthetic culture media in 1937 (White, 1937, 141, 143, 144, 180, 181, 231, 1939, 182, 1940, 172, 173, 232), and to the pro- longed cultivation of undifferentiated plant tis- sues in 1939 (White, 1939, 78).”

The only universally necessary member of the vitamin group seems to be thiamin (vitamin B1).

“The only universally necessary member of this group seems to be thiamin (vitamin B x ) (Bonner, 1937, 198, 199; Robbins and Bartley, 1937, 222, 223 ; White, 1937, 231 ; Gautheret, 1938, 69 ; Nobecourt, 1938, 75).”

Cultures should never be exposed for long periods to direct light because they are extremely sensitive to high temperature and temperature changes and could easily become overheated.

“They should never be exposed for long periods to direct light as they are extremely sen- sitive to high temperature and to temperature changes and could easily become overheated (White, 1932(White, , 63, 1937, 265) , 265) .”

Root tips of wheat have an optimum temperature of about 27°C, and tomato nearer 30°C.

“Root tips of wheat have an optimum temperature of about 27° (White, 1932, 63), tomato nearer 30° (White, 1937, 265).”

Cultures maintained in an ordinary laboratory room without air-conditioning show a marked seasonal variation in growth rate.

“Cultures maintained in an ordinary laboratory room without such control show a marked seasonal variation in growth rate (Fig. 26) (White, 1937, 265) and may, in extreme weather, suffer serious injury.”

In many types of tissues, the requirement for thiamin becomes evident in complete failure of the cultures if thiamin or thiazole is not included in the nutrient.

“In many types of tissues, this requirement becomes evident in com- plete failure of the cultures if thiamin or thiazole is not included in the nutrient (Bonner, 1937(Bonner, , 198, 1938, 199; Robbins and Bartley, 1937, 222, 223; White, 1937, 231, 1939, 182 ; Bonner and Devirian, 1939, 205).”

All cultures except those maintained at 35° and 40° show an immediate reversion to the growth rate typical for 22° after transfer to 22°C.

“All except those maintained at 35° and 40° show an immediate reversion to the growth rate typical for 22°.”