SHRUBS AND TREES 
i57 
The evergreen trees and shrubs of the damper tropical 
regions do not form true resting-buds but vegetate all the 
year round, though commonly exhibiting a regular periodicity 
in the unfolding of new leaves, flowers, &c. The buds of 
young leaves require more or less protection from radiation 
and the accompanying dangers of too rapid evaporation or 
decomposition of the chlorophyll. A very frequent pro- 
tective feature noticed in tropical plants is the red colour 
of the young leaves, well seen in Cinnamomum, Haema- 
toxylon, &c. ; as the leaves get to their full size the chloro- 
phyll developes. The young leaves commonly hang down- 
wards, so that they receive less radiation, and straighten up 
as they become mature, e.g. in Bauhinia, Dryobalanops, 
Cinnamomum and many others ; this may also be seen 
in Aesculus and other temperate plants. In Brownea, 
Amherstia, &c., the whole young shoot droops. In Arto- 
carpus, Dipterocarpus, Ficus, &c., the stipules protect the 
bud ; in Manihot the petioles of the young leaves curve 
upwards and inwards over the bud; in Tabernaemontana 
the bud is protected by the bases of the older leaves, which 
secrete a resinous substance, and so on. 
Many trees flower only at intervals, when they have 
saved enough reserve-materials to supply the flowers and 
seeds ( cf. Agave, above). The beech is an example among 
deciduous trees ; others are Bambusa, &c., and Corypha 
and other palms which only flower once and then die. 
As their height increases, most shrubs and trees grow 
also in thickness, usually by means of the cambium layer 
in the vascular bundles, which adds new wood to the outer 
side of that already existing, and new phloem to the inner side 
of the old phloem. In the great majority of trees, a cross 
section of the trunk shows distinct rings of growth in the 
wood, due to contrast of texture in the new wood formed at 
different times. In temperate climates the contrast is 
between autumn and spring wood, and the ring may be 
termed an annual ring , one being formed each year of 
the tree’s life. In tropical climates with two wet seasons 
a year, many trees form two rings annually ; others form 
rings only when they drop their leaves and form new ones, 
and so on. In dry subtropical climates, the contrast is 
between early dry-season and early wet-season wood. The 
