' i - T. i_ f y 
22 James Small. 
Ecology of llw Tribes. 
The causal relationship of a number of ecological conditions 
to the arborescent habit, the spiny habit, the cushion and espalier 
habit, and other plant forms in the Compositae, can be taken as 
proved to a degree of comparative certainty. 
Scapigerous Perennials. In the grasslands herbaceous peren¬ 
nials are the chief type and, as in Senecio, this type tends to 
become dwarfed, scapigerous, and finally uni-capitulate in the 
alpine and arctic regions. The origin of the Cremanthodium from 
the Ligularia type of Senecio (see Chapter II, E) seems to be almost 
entirely due to the arid alpine conditions of the screes which form 
the typical habitat of that genus^ 
Scramblers. The climbing or scrambling habit is clearly due 
to the direct action of the environment (see Henslow, 38, p. 44) 
and Cockayne gives some very good evidence for this explanation 
(15, p. 21). The presence of open forest or scrub is necessary for 
the development of the typical Composite scramblers. These are 
most abundant on the western margins of the Brazilian forests 
and in the tropical African scrub. 
Erect Shrubs. The erect shrubby forms of the Andes are 
probably the effect of an aridity of environment which does not 
obtain in the Cordilleras, with the result that the shrubby Com¬ 
posites are not so common in the northern region. Quite a number 
of genera with many arborescent species in the Andes are 
represented in the Cordilleras by perennial herbs. The erect 
shrubs reappear at high altitudes in tropical Africa and more 
abundantly in South Africa (cp. 6-7), Australia and New Zealand, 
where the ecological conditions are somewhat similar to those of 
the Andes. The shrubs peculiar to so many oceanic islands are 
probably also the result of the direct action of aridity, wet and cold, 
or hot and dry conditions (cp. 50-51), 
Trees. The large shrubs and trees are obviously the extreme 
development of the shrubby condition. These trees usually occur 
as more or less isolated specimens high up on the mountain sides 
where there are open associations and consequently very little 
competition, and where all the ecological conditions tend to slow 
growth and lignification. The trees of the oceanic islands have 
long been objects of interest, usually regarded as relics of an 
ancient flora, but in the light of the new views on the origin and 
dispersal of species they are to be considered as more or less 
recent species which have become arborescent under the influence 
of external conditions. In addition most of these species have lost 
