274 MORPHOLOGY. 



whole, surrounding the axis. If the lateral production of cells 

 is small, and the union takes place relatively early, this closed por- 

 tion forms a longer or shorter sheath, closely embracing the axis 

 (vagina clausa), as in many Grasses. If, on the contrary, the lateral 

 cell-production or expansion is considerable, and occurs relatively 

 late, so that merely the base of the leaf forms a flat projecting 

 border round the axis, the leaf is said to have the stem growing 

 through it (folium perfoliatum), e. g. Bupleurum perfoliatum. 

 When the axis is angular, and produces thin, more or less projecting 

 plates upon these angles (the so-called winged axis, axis alatus), a 

 similar process may enter into the bud in such a way that a flat leaf 

 is connected at its base with the simultaneously-developed wing or 

 angle of the axis, so that the full-grown leaf appears to be directly 

 continuous with this. Such a leaf is said to run down the axis 

 (folium decurrens), e. g. in Carduus, or, by a wholly unfounded 

 fiction, a leaf blended by growth with the axis (axis folio adnatus). 

 Where several leaves arise simultaneously, or almost simultaneously, 

 at about the same height upon the axis, the bases of the leaves be- 

 come gradually approximated during development ; and here it may 

 readily happen that they approach so close that the same process 

 occurs between the bases of two different leaves, as has been 

 already described in the two borders of one and the same leaf. 

 Thus it happens, then, that leaves, which in their origin and at their 

 summits are free and isolated, in their ulterior development and at 

 their bases form an undivided whole (leaves grown together, folia 

 connata). The leaves of Lonicera Caprifolium afford one of the 

 examples simplest and easiest to trace. Two foliaceous organs 

 which originate one above the other on the same axis (e. g. petal 

 and stamen), or a leaf and the bud developed in its axil (e.g. the 

 bract with the flower- stalk in the Lime), may grow together one 

 above the other, in the same way. 



Lastly, a process almost diametrically opposite to this may occur, 

 where, namely, a leaf is developed, but becomes suddenly arrested 

 in its development in a way yet unknown, whether through mere 

 mechanical pressure or some other cause, by the more rapid and 

 powerful development of the contiguous leaves ; so that either the 

 little original papilla escapes notice, on account of its relatively 

 minute size in the full-grown part, or the little prominence actually 

 becomes effaced by the subsequent development of the part, or, 

 finally, the little rudiment of a leaf dies and gradually decays. In 

 this case the leaf is said to be abortive : an instance easily traced is 

 afforded by the third perigonial leaf of Carex, which aborts in this 

 way, while the two others form the so-called utriculus. And not only 

 may whole leaves become abortive in this way, but even individual 

 portions of a leaf of which the rudiments already exist : thus it is 

 not at all rare for the so-called stipules to become disproportionately 

 developed in the rudimentary leaf, while the proper lea restrained 

 in its growth, gradually disappears from sight. The bud-scales 

 (r amenta} on the perennial buds of Corylus avellana may serve as 



