GENERAL PAPERS 126 
These groupings are called Plant Associations and the fact 
that different associations follow each other successively is 
expressed in the term ‘Plant Succession.” 
C. Special Ecology of Structural Groups. 
While all ecological groups have more or less specific re- 
actions which are considered under their appropriate heads, 
there is one grouping which demands separate treatment 
because it is based on the most striking structural feature— 
the presence or absence of woody tissue, and also because of 
its practical relation to man’s activities. Although verging 
more closely on agriculture, it may still be classed as ecology 
because the point of approach is from the side of the environ- 
mental relations. On the basis of woody structure we classify 
plants as trees and herbaceous plants with shrubs and lianas 
Occupying an intermediate position, and it is at once evident 
that these two groups have decidedly different ecological 
reactions. 
1. Ecology of Trees and Shrubs. This study would in- 
volve (a) a description of leading species with their habits of 
growth, characteristic structures, and ecological interpretation 
of the same. This would be the autecology of the group. 
(b) The synecology would involve the distribution and range 
of the leading species and their relation of ecological causes. 
(c) We might notice also the influence of the species on their 
environment, as illustrated in the influence of forests on soil 
moisture content through their control of run-off; and the 
influence of individual trees, as for example, the eucalyptus 
in the reduction of soil water; also the influence of forests on 
soil in the formation of humus and the effect of trees on wind, 
as in protection by wind breaks, (d) It could include also a 
classification of trees according to the character of their wood, 
including distribution of the different woods and methods of 
utilizing. Also a similar classification according to the char- 
acter of their fruits, their chemical products, and their value 
for ornament. 
2. Ecology of Herbs. Here should be studied (a) the gen- 
eral characteristics of herbs as distinguishing them from trees, 
with the ecological differences involved under the heads of 
shoot, root, flower, and fruit, with the characteristic differ- 
