258 CONTROL OF REPRODUCTION 



than the component cells of the peripheral zone and the pith rib mother 

 cell zone. If one follows the fundamental belief that, siven the same 

 heritage of size initially, larger cells are larger because they have grown 

 more, and that such increased growth implies a greater net availability 

 of growth hormones at the time of growth, then one has to admit that 

 the cellular environment of these central cells must be different from 

 that of the enveloping cells of the peripheral zone. It may well be true 

 that the conditions which foster frequent cell divisions in the peripheral 

 zones are different from those which produce only occasional cell 

 divisions in the central zone (Figs. 1, 2), and even these occasional 

 divisions are more frequent on the margins of the central zone than in 

 the middle. In fact, it is not improbable that these two situations are 

 related causally. As far as the authors know, no one yet has been 

 able to devise methods which have given answers to the problems 

 suggested here at the level at which the plant resolves them. We believe 

 such methods may yet be devised. 



Some facts have proved suggestive. Histochemical tests for oxidases 

 and dehydrogenases give indication of greater amounts of both in the 

 mitochondria of the cells of the central zone over those in the 

 peripheral or pith rib meristem zones. Janus Green B, as found 

 effective by Sorokin (1938, 1941, 1955a,b, 1956a,b), was used on 

 longitudinal sections of the apex. The bluish stain was especially 

 prominent in the central zones of sections immersed in well-oxy- 

 genated isotonic sugar solutions. Also sections placed in a similar 

 sugar solution with 0.002% neotetrazolium chloride (Nutritional 

 Biochemicals Corp.) (Sorokin, 1956b) and contained in a chamber 

 through which purified nitrogen was passed by bubbling it through 

 the solution overnight gave indication of more reddish granules of 

 diformazan in the mitochondria of the central region than in those in 

 the cells of the peripheral region or the pith rib meristem region. Even 

 when the results can be duplicated, these tests are certainly no more 

 than somewhat qualitative and therefore unsatisfying. At present one 

 can record only a working idea and not a conviction. Other techniques 

 must be brought into effective use before anything more than a 

 suspicion of contrastive metabolic activity can be recognized between 

 the central cells and their peripheral and subjacent counterparts. 



Perhaps the most suggestive results so far recorded in this connec- 



