222 MORPHOLOGY. 



commencement of the vegetative period ; or only for the end, e. g. 

 the flower-bearing stalk ; or for the whole period of vegetation. 



From the embryonic condition forward, leaves are continuously 

 developed at the apex of the axis, and, with minute differences, 

 always closely succeeding one another, so that there is never more 

 than a very short portion of the axis (internode, internodium) 

 between any two contiguous leaves. But the cells composing 

 this internode frequently continue for a short time to produce new 

 cells, until enough are formed wholly to perfect the structure of 

 the internode by their mere expansion and further development. 

 By this more complete development, the internode then either 

 becomes elongated, and thus removes the adjoining leaves to a 

 greater distance apart, or this does not take place, and thus the 

 leaves remain stationed immediately above one another. On this 

 depends the most important of all morphological distinctions in the 

 axial organs that between axes with developed and undeveloped 

 internodes. Axes exclusively composed of developed internodes 

 occur, indeed, only among the Dicotyledons. In all axes with 

 undeveloped internodes alone, in all Monocotyledons, and many 

 Dicotyledons, matters are so constituted, that each succeeding inter- 

 node, instead of becoming elongated, expands in diameter like a 

 disc, and each always to a somewhat greater extent than the pre- 

 ceding, so that thus a sufficiently broad basis is gradually acquired, 

 upon which the axis subsequently rises upward in a cylindrical form 

 by developed or undeveloped internodes. Under these circumstances, 

 however, the base of the terminal bud also naturally grows, and 

 this becomes a cone, of varying length, and of a varying degree of 

 acuteness. In correspondence with this, the undeveloped inter- 

 nodes are usually hollow cones fitting one over another. But they 

 do occur also as true discs, nay, even as discs with a concavity 

 sufficient to render them cup-shaped. 



These two forms of the axis, with developed and undeveloped 

 internodes, and both according to their different duration, may 

 alternate repeatedly in the length of the same axis (and still more 

 in the various axes of a plant become compound by development of 

 buds). This composition is completely defined and limited by the 

 habit (habitus) in every single species of plant. 



At the place where the leaf joins the axis, the node (nodus), this 

 frequently exhibits a peculiar expansion or contraction, or both, 

 and these, sometimes below, sometimes above, the base of the leaf, 

 or at others in both situations. This is most frequently met with in 

 developed internodes, especially where the base of the leaf occupies 

 the whole circumference of the axis, or where several leaves share 

 this entirely among them. Various conditions of structure correspond 

 to these external appearances, and the nodes are therefore divided 

 into : perfect nodes, where the peculiarity just described occurs ; and 

 imperfect, where it does not exist. 



In rare cases a so-called joint or articulation (articulatio) is 

 formed, through anatomical conditions, in the situation of the node, 



