Page:Transactions of the Linnean Society of London, Volume 12.djvu/111

Rh vessels there arc generally several in the cord: in Helianthus multiflorus, however, I have not been able to find more than one, either in the trunk of the nerve above the insertion of stamina, or in the branches of the laciniæ. It will be of some interest to verify this fact (which I by no means give with absolute confidence), both on account of the apparently formidable objection it presents to the theory in question, and also that, in following it up by an examination of the point of division, a clearer idea may be obtained of the ramification of spiral vessels than has hitherto been given.

My second objection to M. Cassini's account is, that he describes the nerves as marginal through their whole length. I have formerly, in the passage already quoted, stated them to be parallel and approximated to the margins of the laciniæ. Perhaps in no instance can the branches be considered as strictly marginal; in many cases they are manifestly distinct from the margins, and in the genus Hymenopappus are further removed from them than from the axis of the laciniæ. In H. scabiosæus there is also an evident inequality of the two branches in each laciniæ, the stronger extending nearly to the apex, while the weaker either entirely disappears before it reaches the stronger, or unites with it considerably below its termination. In H. tenuifolius this irregularity is still greater; one branch being not unfrequently altogether wanting, and even the remaining branch considerably weakened: where this happens a secondary vessel is always produced, though very few flosculi are furnished with five complete middle nerves.

To the fact stated by M. Cassini that the lateral nerves are always simple, I have met with only one apparent exception, in an unpublished species of Madia, where they are connected by a few branches with the secondary or middle nerve, which in this Rh