174 BOTANICAL GAZETTE [ AUGUST 
fallen leaves), effects of living plant coverings on the soil, activity of animals 
and plants in the soil, orographic factors (height, steepness, etc.). 
The third section considers life-relations and plant-societies under the fol- 
lowing subjects: life-relationship of living beings, encroachment of man, 
life-relationship with animals, life-relationship of plants with each other 
(parasitism, helotism, mutualism, epiphytes, saprophytes, and lianas), com- 
mensalism (plant-societies), classes of societies (amplified in the succeeding 
chapters). aC 
In section four the hydrophyte societies are considered, the ecological 
factor being air, light, heat, food-stuffs, specific weight, color, and movements; — 
the structural adaptations noted being in roots, water-conducting vessels, 
mechanical tissues, air-cavities, epidermis, slime, etc. The different classes — 
of hydrophilous societies are grouped as follows: free-floating or swimming; 
fixed to the soil, with submerged or floating leaves; and swamp forms. 
Under the first heading there are four categories, the plankton, glacial plant 
unions (ice and snow), saprophilous flagellate unions, and hydrocharité — 
unions (littoral fresh-water free plants). Under the second heading (fixed ; 
to soil, with submerged or floating leaves) are plants fixed to stones (nereid- : 
unions), and those fixed to loose soil (sea-grass vegetation, fresh-water vee : 
tation, and schizophyte unions. Under the third heading (swamp plant-socieé 
ties) the subdivision is into salt water (mangrove vegetation) and fresh wit = 
(reed-swamps, swampy moors, sphagnum moors, sphagnum tundras, swampy a 
thickets and woods). Each of these fourteen categories is fully discussed, 
all the known factors in each situation being considered. a 
Section five is devoted to xerophyte societies, which involves & hac 
cussion of the adaptations for regulating transpiration and for collecting and 
preserving water. Under the regulation of transpiration the titles are p® 
surface reduction, movements for regulating light, constant profile po 
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