i 4 4 
GEOGRAPHICAL DISTRIBUTION 
Ficus elastic a. The most remarkable drip-tip is that of 
Ficus religiosa ; others occur in Acer, Artocarpus, Begonia, 
Boehmeria, Theobroma, &c. Many tropical fruits exhibit 
similar apices, e.g. Kigelia, Mucuna. These leaves are 
generally pendulous with the point downwards, and have 
usually entire margins ; they form the class of leaves 
termed by Jungner rain-leaves . He proposes a second class 
of dew-leaves , occurring chiefly at the boundaries of deserts 
and steppes ; they slope upwards so that water flows from 
them towards the stem, are obovate, and sessile or shortly 
stalked. A third class is the snow-leaves (see Alpine plants, 
below) 1 . 
Wind tends to increase transpiration and in very windy 
places plants occur with a certain amount of extra protect- 
rion against evaporation. Wind also dries the soil and thus 
tends to check absorption of water by the roots. 
All these agents are more or less markedly periodic in 
their action, and in nearly all plants there is a periodicity in 
the life history corresponding to that of the geographical 
agents. In temperate climates this is chiefly- determined by 
the temperature, vegetative activity ceasing in autumn to 
be resumed in spring. In sub-tropical climates (e.g. that of 
the Mediterranean coasts, &c.) the interruption of vegetative 
activity occurs in summer when the heat is great and the 
drought extreme. Even in tropical climates proper, with 
comparatively uniform weather, most plants show a periodi- 
city in the formation of new leaves, flowers, &c. The study 
of the periodic phenomena of vegetation — dates of flowering, 
fruiting, &c. — is termed phaenology. The periodicity is not 
merely annual but also daily, as instanced by the phenomena 
of growth, &c. Removal of a plant to a region of different 
climate does not at once or necessarily destroy the periodi- 
city, which is hereditary and ingrained ; this is illustrated by 
the way in which plants from the southern hemisphere 
continue to flower in our conservatories during the winter 
months of our year, corresponding to the southern summer. 
At the same time the periodicity is not as a rule unalterable, 
and acclimatisation of plants, or alteration of their periodi- 
1 Stahl, Regenfall und Blattgestalt , Ann. Buitenz. 1893 ; Jungner, 
Klima und Blatt in der Regio Alpina , Flora 1894; Wiesner in Sitzb. 
k. k. Akad. Wien, 1893, 1894. 
