226 MORPHOLOGY. 



quadrangular, &c., stems. This condition is most striking when the process 

 of formation ceases very soon on two sides, so that a two-edged stem 

 is thus formed, which very often represents quite a thin plate, and is 

 frequently taken for a leaf, on account of the mistaken notion of regarding 

 the conditions of dimension in space as among the characters of special 

 organs. The best examples are afforded by Ruscus and Phyllanthus. 



D. If it endures longer at the circumference than in the middle, 

 the following results present themselves. In the usual conical form of 

 the terminal bud, the process of cell-formation does not in this case occur 

 throughout the whole cone, but only in its outer layers, so that the 

 whole free surface of the cone contains the youngest cells : the whole of 

 the core of the cone is made up of the older. Here the axis usually rises 

 upward in a cylindrical form, not, however, by means of discs equally 

 deposited upon one another (as in A\ but by hollow cones applied over 

 each other. Every new internode is itself a hollow cone of this kind, and 

 therefore cannot be detached from the axis by a vertical section ; it can 

 only be removed by a section following the course of a conical surface. If 

 the process of cell-formation persists somewhat longer in the succeeding 

 internode than in the preceding, a longer hollow cone is produced, which, 

 consequently, stretches out over the base of the former, which should 

 properly be free ; and thus the new internode becomes broader in pro- 

 portion to the former, so much so, that the free borders of the successive 

 internodes, instead of lying in a vertical cylindrical surface, form a hori- 

 zontal surface (e. g. very often to be observed in Melocactus\ or, in 

 smaller degrees of projection, lie in a hemispherical surface, having its 

 convexity directed downwards (as, for instance, is seen in most stems 

 which are tolerably thick and enduring, in the first or next succeeding 

 internodes, e. g. in Zea Mays, &c.). 



E. Finally, the forms become most striking where the cell-formation 

 ceases at the border earlier than in the centre ; directly the opposite of 

 what occurs in D. This seldom happens in a single internode ; it is usually 

 found where several very short, undeveloped ones, united together, form 

 but a mere disc. When, for example, a disc or a bluntish cone has 

 originally been formed, and the extreme margin loses the power of de- 

 velopment, while the newly forming cells in the middle continue to ar- 

 range themselves into a flattened form, the border will at first be capable 

 of yielding to some extent by the expansion of its cells ; but this soon 

 ceases, and it must become elevated, while the centre gradually developes 

 itself, into a hollow form, in the same way as a plate of lead becomes* 

 hollow when it is beaten out in the middle, and not at the edges. Ac- 

 cording as the time the process of cell -formation lasts, proceeds quickly 

 or slowly, and according as the arrangement of the newly produced cells 

 is restricted a longer or shorter time to the same plane, does the exca- 

 vated form become very different. From the quite convex internodes 

 which bear the florets in Anthemis, through the flat disc of ffelianthus, 

 the concave disc ofDorstenia, to the longish cup-shaped disk, almost closed 

 above, of Ficus, we meet with almost every possible gradation ; in like 

 manner we see the same from the convex fruit-bearing internodes of Po- 

 tentilla, through the cup-form in Rosa, to those completely closed and 

 blended with the ovaries in Mains and Pyrus. So that it may be clearly 

 seen, and I here call particular attention to the fact, that, in all these 

 hollow forms, the deepest point in the interior of the cavity corresponds 

 to the terminal shoot ; consequently it lies indeed mathematically lower, 

 but organically higher, on the axis than the internal walls of the cavity 



