192 



PLANT KELATIONS. 



forests are made of dense growths of hemlocks, pines, etc. 

 In the densest of these forests the shade is so complete 

 that there may he very few associated plants occurring in 

 strata hetween the sphagnum moss and the trees. In the 

 larch forests, however, the undergrowth may be very dense. 



B. Salt-water associations. 

 142. Mangrove swamps.— This is certainly the most 

 vigorous of the salt-water associations. Mangrove swamps 

 occur along flat tropical seacoasts, where the waters are quiet. 



Fig. 166. A mangrove forest advancing into the water.— After Schimper. 



The mangrove is a tree of curious habit, which advances 

 slowly out into the water and extends back landwards as 

 low woods or thickets (see Figs. 166, 167). The whole 

 surroundings appear forbidding, for the water is sluggish 

 and mucky, covered with scum, rich in bacteria, and with 

 bubbles constantly breaking upon the surface from decay- 

 ing matter beneath the water. The mangrove has the pe- 



