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 Catesbcea. 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. Labiatse fur- 

 nish the most striking examples of this structure. I am 

 not however acquainted with any instance of a calyx 

 having five nerves only, and those alternating with its 

 segments. 



The (Estivation or condition of the corolla before expan- 

 sion is the subject of my second remark on Compositse. I 

 87] have, in the observations formerly quoted, stated this to 

 be valvular, 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 PiUo- 

 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 iu 

 Ht/menopappus, are quite simple in the ungues, and ramify more or less in the 

 laminee, near the top of which they unite with each other and with the middle 

 nerve. 



