Culture Techniques 133 



that under these circumstances all members of such 

 a clone could be counted on to behave exactly 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). It does not, however, appear to be the case 

 with cultures of excised roots (Bobbins and Bart- 

 ley, 1937, 170; Bobbins and Schmidt, 1938, 60, 

 1939, 61; Bobbins and V. B. White, 1936, 62; 

 Delarge, 1938, 280, 1939, 281). Sister cultures, 

 placed under supposedly identical conditions, may 

 behave in markedly different manners. This is 

 one of the most disconcerting phenomena encoun- 

 tered in the field of plant tissue cultures. In 

 mycological and bacteriological studies, the inocu- 

 lation of two fragments of mycelium or two bac- 

 terial cells can be counted upon to give rise to 

 colonies of like appearance, aside from the rather 

 infrequent occurrence of saltations. Why is this 

 not equally true of root segments of higher plants? 

 The difference is probably more apparent than 

 real. When a fragment of fungus mycelium is 

 transplanted, it branches rapidly to form a discoid 

 or spherical colony, the outline of which is delim- 

 ited by many hundreds of branches, each of which 

 has its own particular increment rate. The col- 

 ony derived from a bacterial transplant or a frag- 



