ORIGIN AND SIGNIFICANCE OF SPINES 87 



plaut life presenting evidences of a deficiency of growtli 

 force. 



The great groups of plants commonly known as brambles 

 and climbing plants appear to meet most of the requirements. 

 They abound in regions where the greatest luxuriance of 

 vegetation is found, and are therefore chiefly characteristic 

 of the tropics. Kerner^^ estimates that there are two thou- 

 sand species of the true climbing plants in the torrid zone, 

 and about two hundred in temperate regions. Tropical 

 America has the largest number of species, the flora of Brazil 

 and the Antilles being especially rich. In the sombre depths 

 of the tropical forest the climbing plants, or "lianes," are 

 not so abundant as in the open glades and along the edge 

 of the forest, where the amount of light is greater and the 

 conditions of existence are more favorable. As far as rich- 

 ness of soil, amount of light, and degree of temperature are 

 concerned, it must be admitted that their environment is as 

 favorable as that of any of the associated plants having dif- 

 ferent habits of growth. The difference between the strong 

 and erect plants and the comparatively weak and climbing 

 forms is therefore not an extraneous one. It resides within 

 the plant structures themselves, and is an intrinsic character 

 or an expression of hereditary vital forces. 



The law of recapitulation demands that each individual 

 during its development shall pass through an epitome or 

 recapitulation of its ancestral history. In view of the fact 

 that the young seedlings of climbing plants and brambles 

 have the erect form and proportions of normal erect foliage 

 stems, it is safe to infer that they have been derived from 

 erect forms. Further evidence is afforded from the absence 

 of climbing plants in the earlier terrestrial floras. It is 

 obvious, therefore, that they have been developed out of 

 erect forms by a process of degradation. 



The next striking feature to be noticed in climbing plants 

 is their extreme slenderness, due to the general suppression 

 of the plant body. They may attain lengths not reached by 

 the highest trees, and yet the diameter of the trunk is but 



