THE ROOT 73 
(Fig. 52) that form the home of myriads of bacteria, 
which, as we shall see, help the plant to get the nitrogen 
it needs. 
The roots of the mangrove have remarkable 
peculiarities to adapt them to their semi-aquatic 
habit. In the first place a number of so-called prop- 
roots are produced by offshoots from the stem growing 
downwards and fixing themselves in the mud to stay 
L. Cockayne, Ph.D., F.R.S. 
Breathing roots and young plants of Mangrove (Avicennia officinalis). 
the plant and form a buttress against the violence of 
storm or tide. Then, at some distance from the base 
of the stem, are produced green upright growths which 
are really root-tips, that, because of their unusual 
environment, have become negatively geotropic to 
perform new functions. Not only do they break the 
foree of the waves, but, by means of pores, with which 
they are plentifully supplied, provide for the ingress 
of the air to the parts below water. They are really 
breathing roots. Being green, they also, doubtless, 
