In many of these cases it is difficult to say whether the cup-like or tubular form is due to a dilatation or hollowing out of the organ affected, or to a fusion of its edges. The arrangement of the veins will in some cases supply the clue, and in others the regularity of form will indicate the nature of the malformation, for in those instances where the cup is the result of expansion, its margin is more likely to be regular and even than in those where the hollow form is the result of fusion.
=Cohesion of several organs by their margins:--leaves, &c.=--The union of the margins of two or more different organs is of more common occurrence than the preceding, the leaves being frequently subjected to this change. Occasionally, the leaflets of a compound leaf have been observed united by their margins, as in the strawberry, the white trefoil, and others. Sometimes the union takes place by means of the stalks only. I have an instance of this in a Pelargonium, in _Tropæolum majus_, and _Strelitzia regina_; in other cases, the whole extent of the leaf becomes joined to its neighbour, the leaves thus becoming completely united by their edges, as in those of _Justicia_, _oxyphylla_.[22] M. Clos[23] has observed the same thing in the leaves of the lentil _Ervum lens_, conjoined with fasciation of the stem, and many other examples might be given. Some of the recorded cases are probably really due to fission of one leaf into two rather than to fusion. Although usually the lower portions of the leaf are united together, leaving the upper parts more or less detached, there are some instances in which the margins of the leaf at their upper portion have been noticed to be coherent, while their lower portions, with their stalks, were completely free.[24]
Cohesion of the leaves frequently accompanies the union of the branches and fasciation as might have been anticipated. Moquin cites the fenestrated leaves of _Dracontium pertusum_, as well as some cases of a similar kind that are occasionally met with, as instances of the cohesion of the margins at the base and apex of the leaf, which thus appears perforated. This appearance, however, is probably due to some other cause. When the leaves are verticillate and numerous, and they become coherent by their margins, they form a foliaceous tube around the stem. When there are but two opposite leaves, and these become united by their margins, we have a state of things precisely resembling that to which the term connate is applied.
