James Small. 
158 
becomes, therefore, particularly important, and as there is least 
variation in the essential parts of the flower these must be considered 
more important than the very variable non-essential parts. This 
was recognised by the first synantherologist, Cassini, and is 
confirmed by Bentham, the only other botanist who has studied the 
Compositae sufficiently profoundly to express a sound and independ¬ 
ent opinion. 
After dealing with the history of the Compositae we shall, 
therefore, consider the variation in the form and structure of the 
styles and stamens. As these are closely connected in the work of 
pollen-presentation the development of that mechanism, including its 
susceptibility to stimuli, is of first importance. 
The variations in the corolla are considered in relation to the 
floral development and insect visitors; the variations in the pappus 
are considered in relation to the component parts of the trichome 
and the dispersal of the seeds. The characters of the receptacle 
and involucre are considered in relation to their development as 
indicated by closely allied forms of receptacle and involucre and in 
relation to the lines of evolution suggested by the examination of 
less variable parts of the capitulum. The various phylogenetic lines 
indicated by the critical examination of these floral characters are 
tested by the geographical distribution of the groups and the 
phyllotaxis and cytology of the family are found to follow the phylo¬ 
genetic lines established by the preceding investigation. 
In the discussion of the inter-relationships of the tribes and 
genera, use is made of the modern theories of heredity, evolution 
and geographical distribution. Some of these may be regarded as 
rather speculative, but their use is considered justified by the coherent 
account of the evolution of the family which results. Lines for 
further research are abundantly indicated and correction or confirm¬ 
ation of the views expressed will be sought along the various lines of 
physiological relationships, cytological and geological development 
and the details of geographical distribution. 
