INTRODUCTION. 339 
he on many occasions proposed two, or even three, for the same 
genus, leaving future botanists to take their choice. 
Robert Brown, in his memoir in the twelfth volume of our 
Transactions, with his usual accuracy, elucidated many obscure 
points in the structure and affinities of several genera of the order, 
here as elsewhere indicating even much more than he expressec 
in detail, but did not touch upon the general arrangement or 
distribution of the genera. 
David Don, in the years 1828 to 1832, published in the Edin- 
burgh New Philosophical Journal and other periodicals, as well 
as in our own Transactions, various monographie papers on Com- 
posite, chiefly on Cichoriacee and on South-American Mutisiacew 
and a few others. In his new genera he made use of some 
neglected characters derived from the venation of the corolla &e. 
but he seems to have consulted but very little the works of his 
predecessors, and to have been quite unaware of the important 
peculiarities of the style pointed out by Cassini. 
Lessing, after some preliminary papers in the ‘ Linnea,’ published, 
in his ‘ Synopsis Generum Compositarum,’ a new arrangement of 
the order, founded, still more than Cassini’s, upon the modifications 
of the style, proposing many alterations in Cassini’s groups, which 
cannot always be considered as improvements, except in so far as 
they resulted from a command of more ample materials. Cassini’s 
tribes and subtribes are generally natural, although his genera are 
often species only.  Lessing's tribes and subtribes are very 
technical, whilst the main characters are not always sufficiently 
absolute to give them the advantages of an artificial classification ; 
and in his genera he often relies too much on the pappus, the 
variations of which are less in conformity with general differences 
than those of almost any other organ. 
De Candolle, when he arrived at the Composite for the * Pro- 
dromus,' had before him far more extensive collections than any 
of his predecessors. He had in former years worked out mono- 
graphs of some portions of the order ; and he now set to work, with 
his usual ardour and methodical mind, to the diagnosis and 
systematic arrangement of a mass of species nearly equal in num- 
ber to those of the whole vegetable kingdom known in the days of 
Linnsus. But a severe attack of illness came on shortly after he 
had commenced ; and on resuming work after the lapse of a couple 
of years, although his ardour and perseverance remained, he was 
no longer so well able to grapple with complicated difficulties. 
