83 
natural Family of Flants called Composite. 
vessels there are generally several in the cord : in Helianthus mul¬ 
tiform , 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 lacinioe. 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 ob¬ 
tained of the ramification of spiral vessels than has hitherto been 
given. 
My second objection to M. Cassini’s account is, that he de¬ 
scribes the nerves as marginal through their whole length. I have 
formerly, in the passage already quoted, stated them to be pa¬ 
rallel and approximated to the margins of the laciniae. Perhaps 
in no instance can the branches be considered as strictly margi¬ 
nal ; in many cases they are manifestly distinct from the mar¬ 
gins, and in the genus Hymenopappus are further removed from 
them than from the axis of the lacinia?. In II. scabiosaus there is 
also an evident inequality of the two branches in each lacinia, 
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 II. tenuifoliiis this irre¬ 
gularity is still greater; one branch being not unfrequently alto¬ 
gether wanting, and even the remaining branch considerably weak¬ 
ened : 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an unpublished species of Madia , where they are connected by a 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 
m 2 plant 
