POTENTIALLY UNLIMITED GROWTH OF EXCISED TOMATO ROOT TIPS IN A LIQUID MEDIUM

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).”

In 1934 White and Gautheret gave new impetus and orientation to the subject, White by demonstrating the possibility of growing isolated roots for unlimited periods in vitro, Gautheret by demonstrating the possibility of obtaining in vitro growth of fragments of cambium.

“1934-1939 In 1934 White and Gautheret gave a new impetus and orientation to the subject, White by demon- strating the possibility of growing isolated roots for unlimited periods in vitro, Gautheret by demonstrating the possibility of obtaining in vitro growth of fragments of cambium.”

Sucrose is a completely satisfactory carbohydrate for all plant tissues which have so far been grown successfully.

“Fortunately, the much more easily purified and more stable disaccharide, su- crose, is a completely satisfactory carbohydrate for all plant tissues which have so far been grown suc- cessfully (White, 1934, et seq., 65, 66, 78, 172, 173; Fiedler, 1936, 45; Robbins and Bartley, 1937, 222; Robbins and Schmidt, 1938, 60; Thielman, 1938, 171).”

Viruses of a considerable number of diseases of the mosaic group have been cultivated in excised roots of tomato.

“Viruses of a consider- able number of diseases of the mosaic group have been cultivated in excised roots of tomato (White, 1934, 438, 1936, 439).”

When grown in culture, roots do not undergo secondary thickening.

“When grown in culture, roots do not undergo secondary thicken- ing (White, 1934, 65).”

No method has yet been found for inoculating such cultures, so there is no danger of a virus-bearing culture, once established, becoming contaminated with another virus.

“Interestingly enough, no method has yet been found for inoculating such cultures (they must be isolated from systemically infected plants), so that there is no danger of a virus-bearing culture, once established, ever becoming contaminated with another virus (White, 1934, 438).”