6 MORPHOLOGY OF THE ANGIOSPERMS 



rank, the nodes, are attached. Nodes are often defined as levels of at- 

 tachment of leaves, sometimes as levels of departure of leaf traces. 

 Nodes and internodes are continuous parts of the stem; there is no 

 structural delimitation. A description of "nodal anatomy," for example, 

 necessarily covers much of the structure of internodes. Significant mor- 

 phological differences in the shoot are chiefly those of internal structure; 

 they are discussed under The Anatomy of the Plant Body later in this 

 chapter. 



Ecological modifications of the stem and shoot lie outside the scope of 

 this book, but the short shoot should have brief mention, because, in its 

 extreme form, it involves the morphology of "terminal" leaves. In the 

 gymnosperms, the slow-growing, lateral short shoots of Larix and 

 Ginkgo and the determinate, deciduous short shoots of Pinus are well 

 known. In Pinus monophyUa, the short shoot with a solitary pseudo- 

 terminal leaf resembles a simple leaf. In the angiosperms, similar, but 

 less highly specialized, slow-growing short shoots, with crowded nodes, 

 are characteristic of species of Betula, Pijrus, and other genera. Stems 

 terminating in reduced leaves are occasional in monocotyledons— Po/j/- 

 gonatwn, Streptopus, Disporiim, some bamboos. The species of Uvularia 

 show stages in the loss of the stem apex and origin of a terminal leaf. 



The Leaf. The leaf, commonly called an appendage of the stem, con- 

 sists of two fundamental and more or less clearly distinct parts, the 

 blade, or lamina, and the leafstalk, or petiole. A third part, the leafbase 

 — "leaf cushion," "leaf buttress," "leaf foundation" — has long been recog- 

 nized by many morphologists. (The term leafbase has also been applied 

 to the basal, sheathing part of many monocotyledon leaves, both de- 

 scriptively, to the winged base, and morphologically, to the part de- 

 veloped from the base of the leaf primordium.) 



The leafbase, as a basic part of the leaf connecting petiole and stem, 

 is not clearly defined, structurally. Some interpretations of leaf mor- 

 phology call the leafbase a definite part of the leaf, the part that con- 

 nects petiole and stem, "the base on which the leaf stands." In other 

 interpretations, this base is merely the connecting or transitional 

 region between leaf and stem and not a fundamental part of the 

 leaf itself. The limits of the leafbase are not recognizable, ex- 

 ternally or internally. In Europe and Asia, the leafbase has been 

 generally recognized as an important part of the leaf; in America, 

 it has received little attention. Definitions of the leafbase are loose 

 and various, and often seem remarkable as examples of definitions 

 of a morphological entity: the leaf primordium, the basal part of the 

 leaf primordium, the ontogenetic buttress or foundation of the leaf, the 

 hypopodium, the part of the apical meristem of a vegetative shoot 

 where a leaf arises that has no share in the development of the leaf it- 



