ra. y | © °O we 
K, ~ 4 
‘ -: = 
, } 
The length of life of leaves varies greatly. ‘The leaves os 
7 «& w - ‘ 7, es *. we -_- 
’ ) Sa : $ 7D a - x 5 
at Mg Ae 1, ee Ss ; ie n Lee 
tr 4 ~ te ’ ea. s 
. @ 4 YW 7 ae oe. “ei, Se eS 
vs ane at |S “eh Vy ey lke F je + x 
peths Aas 5. tS ey ey 
\ Ne ae 
af _ 
¢ 
108 ~— Structural and P hystolog ical Botany. me wt conn 
of the majority of plants in temperate climates fall off in the — 
autumn [or are deciduous]; in so-called evergreen trees and 
_. shrubs they persist through the winter, and may even remain 
__ for several years, as in some species of Conifere. $ 
- ‘The green colour which is characteristic of the greater 
- number of leaves is due to a colouring matter contained in 
their cells, chlorophyll (see p. 24). In some etiolated |sapro- 
phytic or parasitic] plants, as Orobanche, it 1s wanting ; in 
_ Others the leaves are variegated or coloured white, red, or 
yellow, in patches. The colour of the leaves of many plants 
changes more or less in the course of the year. ‘Thus the 
leaves of the grape-vine, which 
Fic. 196.—Stem-tendrils of the grape-vine ; 
v in the normal state; v bearing a bunch 
- of grapes. 
are at first green, often turn — 
red in the autumn; while 
those of the copper-beecnh 
are reddest in the spring, 
and afterwards become 
more and more green. 
SUBSIDIARY ORGANS. 
Under this head are 
included a number of struc- 
tures which may be regarded - 
as appendages to the or- 
gans already described. 
They are 1n some cases 
modified parts of the 
stem or leaf, in others a 
special development of the 
epidermis which forms the 
outer covering of plants. 
Among them are /endrils 
or crrhz, filiform struc- 
| , tures which cling round 
- neighbouring substances, and whose function is to enable ~ of 
- weak plants to attach themselves to, and to climb up 
