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James Small • 
in the reproductive parts which differentiated the larger families. 
The arborescent habit of the ancestors of the Angiosperms was 
continued in the new group, so that there were only trees, shrubs 
and woody plants growing on trees, lianes and other climbers, in 
that particular region. Certain of the groups had already sent out 
colonisers which, especially the arborescent forms, had begun to 
make some headway, chiefly in the flat lands which formed the 
bulk of the earth’s surface at that time. This period, in fact, was 
the Mesozoic Pre-differentiation Era of Guppy. 
When the Cretaceous uplift raised the Andes well above the 
tree-limit a new habitat was produced, inaccessible to the trees and 
climbers as such, but offering a clear, unoccupied region to such of 
the climbers as were sufficiently plastic to develop into low-growing 
shrubs. 
Among these plastic plants were the members of the Sipho- 
cainpylus-Centropogon group, which proceeded to colonise first the 
lower and then the higher slopes of the new mountain range. 
Under such altogether strange conditions many epharmonic 
variations took place and the Differentiation Era or Age of Com- 
positse (cp. Guppy) was initiated. The first form of Compositae was 
a low-growing, woody, dwarf plant with the inflorescence and 
flowers of Senecio, as explained in Chap. XI. 
The new form of fruit, with a dispersal mechanism eminently 
suited to the wide, windy, more or less barren, mountain regions, 
combined with the simplicity of the physiological constitution of the 
plant which was its inheritance from the Pre-differentiation Era, 
led to a very large development and wide dispersal of the Senecio 
form throughout the Andine region during the evening of the 
Cretaceous day. A similar form, which, however, may be of much 
more recent origin from the same plexus, is seen in Lysipomia, 
where the calyx persists in a clumsy, leafy form, so that this genus 
possesses no particular means of distribution and is still confined 
to the region of its origin. 
Eocene Period. 
Among the many forms developed by Senecio one of the 
earliest distinct types, Gnaphalium , witli more complete aggregation 
of parts, was produced by the conditions near the snow-line. An¬ 
other of the early types was the result of the re-invasion of the 
lower, more temperate regions by the now very definitely organised 
and aggressive Senecio. The annual and rhizomatous, perennial, 
herbaceous forms of Senecio probably developed in connection with 
