THE PLANT BODY 



self, the connecting tissues of leaf and stem, the region in the stem and 

 leaf where lateral leaf traces change course toward the median trace, 

 the segment of the axis which subtends a leaf initial and surrounds the 

 leaf trace as it differentiates. The failure of American morphologists to 

 recognize the leafbase as an important part of the leaf cannot be under- 

 stood by some Indian morphologists, "because a leaf without a base 

 cannot be conceived." 



Ontogeny provides the best basis for an understanding of the nature 

 of the leafbase. The leaf primordium arises as a lateral, more or less 

 crescent-shaped mound or ridge on the apical meristem of the shoot. 

 From this early primordium, as a base, arise a median conical or 

 cylindrical projection — from which the blade and petiole develop — and, 

 if stipules are present, lateral lobes. If a leafbase is to be recognized, it 

 is recognizable only in shoot ontogeny as the base of the leaf primor- 

 dium; it cannot be distinguished in the mature leaf or node. 



The leafbase has been well described as a primordial region in the 

 young node, consisting of two components — a proximal cauline or axial 

 part, and a distal foliar part. Together, these components form the 

 part of the shoot transitional from stem to leaf, a part not limited in- 

 ternally but sometimes limited externally as decurrent areas of epi- 

 dermal and cortical tissues set apart by unusual color or vesture. This 

 description sets no limit internally in the stem for the leafbase; others 

 set as the limit "to the pith" or "sometimes to the pith"; still otliers 

 "to the center of the pith." Interpretations of the radial extent of the 

 leafbase conflict with morphological distinctions within the stem. If the 

 leafbase tissues extend only to the pith, the leafbase, as a part of the 

 leaf, clothes the pith, or "core," as a "mantle," and the shoot axis con- 

 sists of the pith only; if the leafbase extends to the center of the pith, 

 no axis, as such, exists in the nodal region. Structure of the apical 

 meristem is reported to show that the view that the leafbase tissues 

 extend to the center of the axis is incorrect, because "two different 

 zones of the meristem form mantle and core." The leafbase, if such a 

 structure is worthy of distinction, is a segment of the shoot, not of the 

 leaf. (The extent of the leafbase as a unit of structure of the shoot is 

 further discussed under the leaf-skin theory, p. 21.) 



If the shoot is accepted as one of the two basic parts of the plant 

 body, the leaf can well be called a "partial shoot arising from a parent 

 whole shoot." There is then no necessity to distinguish a part of the 

 shoot, partly stem and partly leaf, as a fundamental part of the leaf. 

 The term partial shoot is good in its implication that the leaf is a lobe 

 of the axis, but not because it has "lost its adaxial part in the develop- 

 ment of the dorsiventral form," as suggested under one theory. The leaf- 

 base is not recognized in this book as a part of the leaf; it is considered 



