THE DICOTYLEDONES 



1775 



spherical woody spheres to which the name " Cannon Balls " has been 

 given (Fig. 1664). 



The family is characterized by the presence of a series of cortical bundles 

 which run up as separate traces into the leaf and remain distinct not only 

 in the midrib but in the larger veins as well. 



The Rhizophoraceae include a number of interesting plants col- 

 lectively referred to as the Mangroves. They form a very characteristic 

 vegetation on muddy coasts and estuaries in the tropics. The family is a 

 small one containing about twelve genera, with some sixty species. They 

 are all woody plants with simple, often leathery, leaves. It is however their 

 tendency to produce large aerial prop-roots, after which the main roots and 

 the base of the stem disappear, which has gained them such a reputation, for 

 these prop-roots (see Fig. 825, Vol. I) form an almost impenetrable jungle, 

 while at the same time lifting the functional stems above the sea at high tide. 

 At low tide they bridge over the evil-smelling estuarine mud. 



The best-known genus is Rhizophora (Fig. 1665) and it is interesting 

 particularlv on account of the germination of the seeds while still attached 



<w 



Fig. 1665. — Rhizophora conjtigata. Leafy shoot 

 with flowers and fruits, the latter showing 

 outgrowing seedlings. Below, similar 

 fruits and seedlings of Briiguiera caryo- 

 phylloides. {After Karsten.) 



Fig. 1666. — Rhizophora nuicro- 

 nata. Fruits with fully 

 developed seedlings at- 

 tached. The middle one has 

 been dropped from the fruit 

 and shows the terminal 

 plumule. 



to the parent tree (Fig. 1666). In section at a young stage the embryo 

 consists of a very large hypocotyl whose free end is directed downwards 

 2 A 



