268 OBSERVATIONS ON THE NATURAL FAMILY
The principal peculiarity, however, consists in the corolla of a syngenesious plant, when reduced to its smallest number of nerves, having these nerves alternating with its segments in the tube. I am acquainted with no instance of this order of reduction in the nerves of any other mono- petalous corolla, but I observe an apparent tendency to it in Portlandia and Catesbaa. In the tube of the corolla of both these genera there are ten nerves, of which the five that alternate with the segments are manifestly stronger, and seem to furnish the greater part of the vascular system of the upper part of the tube and of the segments ; the intermediate nerves being there somewhat like recurrent branches.
I shall conclude this subject by observing, that although the existence of nerves alternating with the segments of a monopetalous corolla, dividing below the sinus and uniting their branches at the apex of the segment, be rare, this dis- position is comparatively frequent in a monophyllous calyx, especially where its aestivation is valvular. Labiatae fur- nish the most striking examples of this structure. I am not however acquainted with any instance of a calyx having five nerves onlv, and those alternating with its segments.
The (estivation or condition of the corolla before expan- sion is the subject of my second remark on Composite. I 87] have, in the observations formerly quoted, stated this to be valvidar, that is, having the margins of the segments applied to each other and dehiscing like the valves of a capsule. As I have remarked in the same place that this aestivation exists in several other families, it is rather sur- prising that M. Cassini, in the abstract of his third memoir given in the Nouveau Bulletin des Sciences for last Oc- tober, should seem to consider this character as peculiar to
actual disposition of vessels in certain polypetalous genera. Thus in Pitto- sporum revolutum, each of the petals has three nerves with distinct origins. Of these the two lateral, evidently within the margins, less so, however, than in Hgmenopappus, are quite simple in the ungues, and ramify more or less in the lamina, 1 , near the top of which they unite with each other and with the middle nerve.
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