*54 
SHR UBS AND TREES 
tection against snails, caterpillars, &C . 1 Glandular hairs 
also probably act as protections of this nature. 
Shrubs and Trees 2 are perennial plants with woody 
stems above ground, and do not entirely die down during 
the period when vegetation is interrupted. Shrubs are 
described as woody plants of not more than about 30 feet 
high, and much branched down to the level of the ground, 
whereas trees have usually one stem at the base which 
branches out above, and generally grow to more than 30 feet 
in height. A sharp demarcation cannot be made, all kinds 
of intermediate forms existing. Similarly between shrubs 
and herbs there occur intermediate forms ; low-growing 
shrubby plants like heather (Calluna) are termed under- 
shrubs , and below these are suffruticose herbs (above). 
A large proportion of the earth is covered with trees and 
shrubs ; in the colder parts of the north temperate zone 
these are mostly Conifers, elsewhere Angiosperms, or some- 
times Ferns. Forests grow best where there is plenty of 
moisture, as in the tropical monsoon region, the Amazon 
valley, and the lower slopes of mountains. 
The majority of trees and shrubs are evergreen , retaining 
their foliage throughout the year ; others are deciduous , 
dropping their leaves in autumn or at the beginning of 
the dry season. In temperate climates the evergreens are 
chiefly Conifers, and the other woody plants are deciduous. 
The former are of monopodial growth, and when growing 
apart from other trees are of more or less conical shape, 
with branches from top to bottom ; in forests the lower 
shaded branches die and fall away and the tree spreads 
out at the top only. The deciduous trees usually show 
a more rounded shape when growing separately {e.g. elm 
or oak), and they do not generally show a single straight 
main stem reaching right to the top ( excurrent ) as in pines, 
but their stems are more or less broken up into branches 
( deliquescent ) at some height from the ground. Most of 
1 Stahl, Pflanzen und Schnecken , Jena, 1889. 
2 Areschong, Beitr . z. Biol. d. Holzgewachse , Lund, 1877 ; Goebel, 
Organography of Plants ; Potter ( Bud-protection ) in Linn. Soc.J. , 1888; 
Keeble ( Hanging Foliage ) in Ann. Bot., 1895 ; Stahl (. Regenfall u. 
Blatigestali) in Ann. Buitenz., 1893 ; Groom ( Bud-protection ) in Linn. 
Soc. Trans., 1893, &c. ; and see below. 
