ECOLOGICAL 167 



advantage is getting out of the crowd rather than getting nearer 

 the Hght. 



Among the common adaptations of epiphytes may be mentioned : 

 (a) structures for absorbing water, e.g. by a spongy tissue covering 

 the aerial roots; (6) structures effecting attachment, e.g. non- 

 absorbing anchoring roots; (c) reduction of transpiration, e.g. by 

 developing of a firm cuticle or by having little or no foHage; and 

 (d) the speciaUsation of seeds for attachment. 



It occasionally happens that a plant perches on an animal, and 

 this association might be called epizoic, were it not that this term 

 is used (hke epidemic) in connection with the spreading of some 

 animal diseases. On littoral animals, such as limpets and mussels, 

 there is sometimes a growth of seaweeds, already referred to in 

 connection with "masking", and a lobster is occasionally found 

 with a thick draping. When the animal is a rapid mover there may 

 be some advantage to the Alga by promoting aeration. Strangest of 

 all linkages of this sort is the occurrence of minute Algae on the 

 rough hairs of the South American Tree-Sloths. 



CLIMBING PLANTS. — Darwin's strong ecological interest, so 

 marked in connection with Insectivorous Plants, was also illus- 

 trated in regard to climbers; see his Movements and Habits of 

 Climbing Plants (1875). As the habit has developed among many 

 different orders of plants and in all parts of the world, there must 

 be some general advantage, which may be described in a general 

 way as escape from crowded struggle and from extreme shade by 

 getting on to the shoulders of other plants. To this it should be 

 added, from our point of view, that the chmbing plant is often 

 marked by a relative weakness of stem which prevents it standing 

 upright, and by the elongation of internodes which facilitates 

 leverage. To others it seems to involve fewer assumptions to suppose 

 that a climbing plant is one which has adapted itself to climbing 

 by using its resources to form large vessels and by effecting quick 

 growth at the expense of lignification. 



We shall follow Darwin's convenient grouping of climbing plants 

 into five grades: scramblers, root-climbers, twiners, leaf-climbers, 

 and tendril-bearers, though there are, as usual, gradations between 

 these. 



Scramblers. — ^The brambles on an old-fashioned hedge or by the 

 side of a copse may serve as a starting-point. With vigorously 

 growing stems, sometimes many yards long, they ramp among the 

 adjacent stronger plants, and they are helped by their spines. There 

 is no special adaptation; the brambles lever themselves on the 

 shoulders of their neighbours. Yet the New Zealand Ruhus sqiiar- 

 rosus is able to climb more vertically, just like Ramblers among 

 roses. The Climbing Palms or Rotangs (e.g. Calamus extensus) have 



