POTENTIALLY UNLIMITED GROWTH OF EXCISED PLANT CALLUS IN AN ARTIFICIAL NUTRIENT

In 1939 White, Nobecourt, and Gautheret independently demonstrated the possibility of growing undifferentiated tissues for unlimited periods, and White demonstrated experimental control of differentiation in such cultures.

“This was capped in 1939 by White's, Nobecourt's, and Gautheret 's indepen- dent demonstration of the possibility of growing undifferentiated tissues for unlimited periods and by White's demonstration of experimental control of differentiation in such cultures.”

The only intercalary meristem successfully grown is that from the procambial region of tobacco.

“The only intercalary meristem which has been successfully grown is that from the pro- cambial region of tobacco (White, 1939, 78).”

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).”

Work of Gautheret, Nobecourt, and White led to the first really successful prolonged cultivation of undifferentiated plant tissues.

“With the work of his com- patriot Nobecourt (Nobecourt, 1937, 74, 1938, 75, 76, 1939, 77; Nobecourt and Dusseau, 1938, 311), and with White's (Fig. 12) independent work in America, these studies have led to the first really successful prolonged cultivation of undifferenti- ated plant tissues (White, 1939, 78, 333) .”

Animal tissue cultures and cultures of undifferentiated plant materials generally behave alike under a given set of conditions.

“This is generally true of animal tissue cultures (Ebeling, 1921, 456; Parker, 1932, 422, 423, 1938, 26) and cultures of undifferentiated plant materials (White, 1939, 78).”

The tendency towards differentiation of scalariform cells in the interior of callus cultures may be looked upon as an example of cellular response to a particular environmental complex, in this case one of low available oxygen content.

“The tendency towards differentiation of scalariform cells in the interior of callus cultures (White, 1939, 78) may be looked upon as an example of cellular response to a par- ticular environmental complex, in this case one of low available oxygen content”

White has shown that an oxygen gradient may be correlated with the response by which undifferentiated callus cultures are induced to form stems and leaves without the intercession of a caulocaline.

“White (1939, 333) has shown that an oxy- gen gradient may be correlated with the response by which undifferentiated callus cultures (Figs.17, 18, 61, 65) are induced to form stems and leaves without the intercession of a caulocaline (Figs.68, 71).”

With plant tissue cultures, the method of imposing or modifying gradients is a virgin field except for White's preliminary observations on oxygen gradients and differentiation and, in a sense, those of Nobecourt and Gautheret on bud formation.

“With plant tissue cultures it is a virgin field except for White's preliminary observations on oxygen gradients and differentiation (Figs.68, 71) (1939, 333, 1942, 334) and, in a sense, those of Nobecourt (1939, 448) and of Gautheret (1940, 286-288) on bud formation.”

White, Gautheret, and Gioelli have made similar studies with callus cultures.

“White (1939, 78) Gautheret (1938, 283, 284) and Gioelli (1937, 290) have made a few similar studies with callus cultures.”