THE ROOT 199 
Photosynthesis (leaf function). Underground roots are not 
exposed to the light, and so are not in a position to carry on pho- 
tosynthesis. Such roots do not develop chlorophyll. The roots 
of many epiphytes and of some vines, however, are exposed to 
the light, and such roots 
usually possess chloro- 





\ AS i \\ 
phyll and so manufac- x ane 
INAWIPSAS\S IVA ‘ 
ture food by means of y AN) I NVI GAAV AO 
. /} EN Vp A y y 
photosynthesis. In the ps \\ 
epiphytic orchid Taenio- 
phyllum (Fig. 195) this AK 
function is performed 
almost entirely by the i ni 
roots. This plant has 
no leaves and only a 
small stem, to which the 
roots are attached and . 
which bears the flower 
shoots. The roots, on the 
other hand, are highly 
developed and contain 
chlorophyll. | 
Support (stem function). 
In a number of cases, 
roots take the place of 
stems in serving as sup- 
ports. This is the case 
in the genus Pandanus 
(Fig. 196), where that 
part of the stem which 
is near the ground is very small and incapable of supporting 
the weight of the plant. Large roots grow out from the main 
stem and serve to brace it; such roots are called brace roots. 
Other roots grow down from the branches and prop them 
up; such roots are known as prop roots. Rhizophora (igs. 197, 
516) has similar brace and prop roots. Corn has brace roots. 


\~ 
pp 
4. 
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Fie. 196. Pandanus tectorius with prop 
roots. (X 35 
