OF PLANTS CALLED COMPOSIT.f;. 265 



ever, connecting with it the ingenious hypothesis of M. 

 DecandoUe, namely, that petals are only modified stamina. 

 It remains to be seen on what ground M. Cassini has 

 adopted this theory, as proposed by M. DecandoUe, for 

 Compositse, the only family which seems to present a very 

 important objection to it, in having its principal, and in 

 the greater part of the order its only, vessels occupying 

 the lines of junction of the supposed united petals. 



To adapt this disposition of vessels to the theory, 

 M. Cassini is obliged to subdivide their apparently simple 

 trunks; a division, however, which may be regarded as 

 entirely hypothetical. Prom the observations I have made 

 on the subject, I have no doubt that these trunks are 

 equally simple with the secondary nerves when present, 

 or with the primary in other families. I find them to con- 

 sist of two kinds of vessels, the spiral and ligneous. Of 

 the spiral vessels there are generally several in the cord : 

 in Helianthus muUiJiorus, however, I have not been able [ss 

 to find more than one, either in the trunk of the nerve 

 above the insertion of stamina, or in the branches of the 

 lacinise. 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 pre- 

 sents 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 lacinise. 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 lacinise. In H. scabioscsus 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 



