260 CONTROL OF REPRODUCTION 



Brown and his co-workers suggest that the higher protein turnover in 

 the large-celled region may conceivably be related to the production of 

 certain mobile substances which are utiUzed extensively in the synthesis 

 of macromolecules made available to the enveloping, dividing periph- 

 eral cells. Although no evidence exists of the similarity in metabolic 

 turnover of the large-celled central zone and the incipient pith of the 

 first four internodes, the results are sufficiently provocative to justify 

 attempts to determine the oxygen uptake of the cells in the central zone 

 of the apical meristem. It is of more than passing note that cells of 

 internodes 5 to 7 show a greatly decreased oxygen uptake from those 

 of internodes 1 to 4. 



The suggestive results of our own cytochemical studies find sup- 

 port in the studies of Sunderland, Heyes, and Brown. A more critical 

 statement of their units in terms of the apical organization of Lupinus, 

 together with an extension of their studies to other plants, may lead to 

 a better understanding of the organization and metabolic behavior 

 of the apices of vascular plants. 



This extended consideration of the vegetative apex has seemed 

 necessary if we are to examine it as that same apex which becomes 

 modified in the production of reproductive devices, whether spore- 

 bearing leaves in the ferns, or cones in the conifers, or flowers in the 

 angiosperms (Figs. 6, 13, 14, 17, 20). Differences of opinion exist 

 (Buvat, 1952, 1955;Gifford, 1956; Gregoire, 1938; Plantefol, 1947, 

 1951) concerning the interpretation of the dramatic changes in the 

 transformation of angiospermous apices from vegetative to flowering 

 conditions. Is the apex gradually and progressively altered, either 

 anatomically or physiologically or both, with the advent of the 

 reproductive period? Or is it replaced by a derived apex which can 

 produce only inflorescence or floral parts? Gregoire (1938) has 

 hypothesized a complete replacement of the vegetative apex with a 

 reorganized terminal portion having a "massif parenchymateux," or 

 a massive central core, covered by a few-celled "manchon meri- 

 stematique," or mantle, of small, actively dividing cells from which 

 the floral organs arise as well as those of the underlying core. To 

 Gregoire, the vegetative and floral apices were "irreducible types" of 

 morphological organization. More recently Plantefol (1947), Buvat 

 (1952, 1955), and their co-workers have fostered the Gregoire con- 



