THE STRUGGLE FOR EXISTENCE 215 
vegetatively. Swamp plants are like hydrophytes in 
their lower submerged parts, but like land plants in 
their upper aérial parts. 
Xerophytes are drought-resisters, and occupy 
chiefly the wind-swept heaths and the sand-dunes. 
Reduced leaf-surface and other adaptations for 
checking transpiration are seen here. 
Xerophytic Hydrophytes live in water or wet 
situations, but, owing to excess of certain materials 
in the water, have to guard against too great water 
absorption and have thus assumed a _ xerophytic 
eharacter. Such plants are found in sphagnum bogs 
and salt meadows. 
Mesophytes require a moderate rainfall, and such 
societies form either forest or grass land, the latter 
requiring a less but more evenly distributed rainfall 
than the former. New Zealand lowland forests are 
rain-forests, and may be mixed forest, kauri forest, 
or kahikatea forest. Ascending the mountains we pass 
through the beech forest, sub-alpine scrub, alpine 
meadow, and finally arrive at the climatic desert at 
the summit. 
QUESTIONS ON CHAPTER VIL 
1. What is meant by the ‘‘Struggle for Existence,’’ the 
‘‘Survival of the Fittest,’’ ‘‘ Natural Selection’’? 
2. What weeds have you found the most persistent? Give 
reasons for this persistence. 
3. What is a weed? Why do garden vegetables need help 
in their struggle for light and food? 
4. Why is the manuka able to establish itself in almost any 
situation ? 
5. How is it that plant societies come to be formed? 
6. What is the chief factor determining the nature of the 
plants forming any particular plant society? What 
other factors may operate? 
7. What conditions give rise to grass-land and what to 
forest? 
