How Cultures Are Started 125 



bial strands. Medullary rays, the multiple peri- 

 cycle, and certain phelloderm cambiums should in 

 theory be fairly satisfactory experimental mate- 

 rial, albeit difficult to isolate. They have appar- 

 ently not been studied to date. There are in 

 plants, of course, many other regions which show 

 meristematic activity. Very young seed pri- 

 mordia are made up entirely of meristematic cells 

 and are easily removed with little danger of con- 

 tamination and a minimum of trauma (White, 

 1932, 89 ; Moebius, 1928, 105; Molliard, 1921, 106). 

 All of the tissues of young ovaries are likewise 

 meristematic as are some of those of more mature 

 ovaries (Tukey, 1937, 114). Wehnelt (1937, 230) 

 and subsequently Bonner and English (1938, 342) 

 have taken advantage of this fact and used tissue 

 from the inner surface of bean pods as material for 

 the study of proliferation. Bonner has had some 

 success with tissue cultures of this material (Bon- 

 ner, 1936, Pi) (Fig. 35). The meristematic centers 

 in the leaves of Begonia, Bryopliyllum (Naylor, 

 1931, 308),Saintpaulia (Naylor and Johnson, 1937, 

 309), Chlorophytum (Naylor and Sperry, 1938, 

 310), Camptosorus, etc., and the stipular gemmae 

 of Marattia should theoretically be excellent mate- 

 rial with which to work but have not been studied 

 as yet. Many "mature" regions may also be 

 stimulated to renewed activity by proximity to a 



