Det 

THE ROOT 203 
Many tropical trees have buttress roots (Fig. 492) which are 
formed by the outgrowth of planklike extensions from the 
upper portions of large roots. Such buttress roots are frequently 
made into table tops. 
Reproduction (seed function). The roots of many plants pro- 
duce adventitious buds which grow into new plants and thus 
serve to reproduce the species. Some 
plants are reproduced artificially by root 
cuttings. 
Storage. Underground roots may be- 
come very much thickened and serve as 
organs for the storage of food. Such is the 
case in sweet potatoes (Fig. 201), yams, 
radishes (Fig. 180), turnips, parsnips, and 
carrots. Roots may also store water. ~ 
Aération. Specialized aérating roots are 
found on a number of plants that grow 
in submerged soil (Fig. 518). These 
are particularly prominent in mangrove 
swamps. Such roots contain a conspicuous 
development of air space. Oxygen from 
the atmosphere diffuses into these spaces 
and then down into the underground root 
system. ‘The aérating roots extend verti- 
cally out of the soil in some mangrove- 
swamp species (Fig. 517), and also in the 
bald cypress of the fresh-water swamps 
of the southeastern part of the United 
States. In the genus Rhizophora (Fig. 197) of the mangrove 
swamps the aérating roots grow from the trunk and branches 
and also serve as absorbing roots and as brace and prop roots. 

Fic. 201. Root of sweet 
potato modified for food 
storage. (xX) 
