30 Tansley and Fritsch. 
end is weighted, helping a direct fall. According to Karsten 1 the 
seedling Rhizophoras first float horizontally, but subsequently 
gradually take up a vertical position as the club-shaped lower 
portion becomes saturated with water. In this way the social 
habit of the tree is established; while at the same time the embryos 
which are carried away are able to resist the salt water for a great 
length of time, and if eventually deposited in a suitable spot 
continue their growth and thus secure the wide distribution of the 
species. Of course many embryos and seedlings perish through 
being left by the water in localities where germination, or at least 
growth into a tree, is impossible. Crossland 2 described a case on 
the coast of Zanzibar, where Rhizophora-e mbryos (evidently from 
his figure R. conjugal a), floating in the vertical position, are planted 
by the falling tide in suitable crevices of the flat limestone rock 
which forms the shore. Here the trees appear to flourish per¬ 
fectly well though there is but a thin coating of mud on the solid 
limestone. This corresponds with Schmidt’s 3 remark (p. 14), that 
R. conjugatci can grow on mud, sand, or even rock, thrusting its 
roots into the crevices. 
The allied genus Bruguiera resembles Rhizophora very closely 
in habit and general appearance and is constantly associated 
with it, but lacks the characteristic stilt-roots-—except very short 
Fig. 9. Young knee root of Bruguiera gyninorhiza. The part bearing laterals 
is embedded in the mud, the upper part shews the scaling periderm 
exposed to the air. The thick spongy cortex is indicated on one of 
the cut ends. Half natural size. 
1 Ber. Deutsch. Bot. Ges., 1900, p. (53). 
3 Annals of Botany 17, 1903, p. 267. 
3 Bot. Tidsskrift, 1904, vol. 26. 
