194 SOME BRITISH PLANT GROUPS 
are conspicuous by their absence. The brief summer 
and long winter are unsuitable to the economy of 
annual plants; and the alpine perennials are so con- 
structed that with the passing away of the cold, 
flowering and fruiting may be accomplished quickly, 
before winter descends again. The abundance and 
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Fic, 34.—NEW ZEALAND SHRUBBY VERONICAS, SHOWING, FROM 
LEFT TO RIGHT, REDUCTION OF LEAF WITH INCREASING 
ELEVATION OF HABITAT. 3. 
vividness of the flowers of alpines is almost proverbial. 
Several explanations have been put forward to account 
for these features, and probably there is some truth in 
each of them. It has been held that the brilliancy of 
the sunlight is accountable; the shortness of the period 
available for seed-production, and the consequent need 
of prompt pollination by insects, have been suggested, 
