HYDROPHYTE SOCIETIES 179 
work of conduction is not so extensive or definite, and 
therefore in such water plants the woody bundles are not 
so prominently developed as in land plants. 
(4) Reduction of mechanical tissues. In the case of 
ordinary land plants, certain firm tissues are developed so 
FIG. 100. Gulfweed (Sargassum), showing the thallus differentiated into stem-like and 
leaf -like portions, and also the bladder-like floats. After BENNETT and MURRAY. 
that the plant may maintain its form. These supporting 
tissues reach their culmination in such forms as trees, 
where massive bodies are able to stand upright. It is evi- 
dent that in the water there is no such need for rigid sup- 
porting tissues, as the buoyant power of water helps to 
support the plant. This fact may be illustrated by taking 
