Small .— Pollen-presentation Mechanism in the Compositae . 469 
The pollen-presentation mechanism is not the only character which 
shows progressive variation in the Compositae, and any phylogenetic scheme 
must take into account the form, development, and colour of the corolla, 
the form of the pappus, the composition of the capitulum, and the 
geographical and geological distribution of the main divisions of the order; 
the available data concerning these characteristics must be increased before 
a satisfactory discussion of the inter-relationships of the tribes can be 
attained. 
Conclusion. 
In dealing with so recent an order, and one which, as a whole, is 
herbaceous, the fossil evidence is scanty and conflicting. Such being the 
case, the somewhat scattered fossil literature of the order awaits critical 
study. 
That the cytological phenomena might be of value occurred to the 
writer early in 1913, and material was afterwards prepared for cytological 
investigation. Since that time the question of correlation between chromo¬ 
some dimensions and phylogeny has been the subject of several papers (14 
and 7 ) which have dealt with the problem in relation to the larger groups 
of the animal and plant kingdoms, and the results already obtained are 
being held over, pending a critical study of a considerable number of closely 
related species. The characteristic more or less spherical forms of the 
chromosomes in most Compositae may be mentioned as one interesting fact, 
in view of the controversial condition of the subject at present. 
In addition to the data which have already been collected concerning 
the floral organs, a number of isolated but relevant observations have come 
under my notice during the four years which I have been working at this 
problem, and although these cannot be introduced readily into such a brief 
and tentative account as the foregoing, all the known facts are quite com¬ 
patible with the origin of the tribes which is suggested as a result of the 
analysis of the staminal and stylar forms. 
Acknowledgements are due to the Regius Keeper of the Royal Botanic 
Garden of Edinburgh for permission to study in the herbarium and for 
fresh material of many species of Senecio ; to Professor M. C. Potter, for 
access to books and periodicals ; to Professor A. C. Seward, for help with 
the fossil literature; to Professor A. H. Trow, Mr. W. Hales, A.L.S., 
Chelsea Physic Garden, and Mr. R. Irwyn Lynch, M.A., University Botanic 
Garden, Cambridge, for material. 
Summary. 
1. The hypothesis that the appendages of the style branches and the 
apical and basal appendages of the anthers are the expression of a tendency 
