THE PLANT BODY 35 



core is "parenchymatous" (not meristematic), because the shoot is de- 

 terminate and cell divisions have largely ceased in the central part. The 

 mantle is wide and complex in structure, because in it are developing 

 the primordia of many appendages. The mantle corresponds to the 

 timica and the outer part of the corpus. Secondly, the floral appendages 

 are claimed to have arisen from more superficial layers than do leaves. 

 This difference does not exist; the wider mantle and the contrast be- 

 tween mantle and core — greater than in vegetative apices, because of 

 more abundant primordia in the outer part and few cell divisions in 

 the center — makes the origin appear to be more superficial. The third 

 claim was that there are no foliar buttresses in the floral apex. But the 

 buttresses develop later and are smaller, because the nodes are crowded. 

 A fourth claim was that development of procambial strands is strictly 

 acropetal in the floral apex, whereas in the vegetative axis development 

 is in both directions from the base of an appendage. But development 

 of the procambium is alike in both kinds of apices. The small size of 

 the appendages at this stage and their crowded arrangement make 

 direction of development difficult to determine. And, finally, it was 

 claimed that carpellary primordia are not crescent-shaped and do not 

 embrace the shoot axis as leaf primordia do. But the carpel primordia 

 of many taxa, those in which carpel closure is postgenital, are crescent- 

 shaped; those in which closure is congenital are not crescent-shaped. 

 The floral apex is morphologically like the vegetative apex; differences 

 are of degree only, associated with differences in function. It is a 

 vegetative axis gradually transformed, not a new structure. Under some 

 growth conditions, the floral axis may be transformed into a vegetative 

 axis, as in terminally proliferated flowers. 



Ontogeny of the Root Apex. The anatomy of the root apex was well 

 known long before critical studies of the shoot apex were made, doubt- 

 less because of the greater simplicity of the root apex and better dis- 

 tinction of histogenetic zones. In the root apex was found, in large part, 

 the basis for the histogen theory, but greater interest in the more com- 

 plex shoot apex has placed acquaintance with this growing point ahead 

 of that of the root. 



Early descriptions of the apical meristem of the root set apart a 

 central core, the plerome; an outer sheath, the periblem; and a uniseriate, 

 outer layer, the dermatogen. Distinction of these layers, with implica- 

 tion of restriction in function and morphology in the parts developed 

 by each, formed the histogen theory. Though better acquaintance with 

 anatomy showed that the terms do not have the morphological value 

 assigned to them, they have continued in use as of topographical value. 

 Tunica and corpus are terms not applicable to the root apex, because of 

 its markedly different morphology. The apical meristem of the root is 



