44 CLIMBING PLANTS [CHAP. 



the anomalies arise as soon as, but not before 

 contact in many cases, we are justified in infer- 

 ring we have a distinct cause and effect. This, 

 moreover, is corroborated by the fact that, plants 

 whose stems are, as a rule, climbers, such as 

 Convolvulus, having nothing to climb up, become 

 creeping herbs, as C. arvensis, or stunted woody 

 shrublets, as are other, species of Convolvulus in 

 the deserts near Cairo (fig. 12). The proba- 

 bilities are greatly increased on the acquirement 

 of climbing by use, and the loss of it by disuse. 

 Many living as shrublets in the desert develop 

 climbing varieties in forests. Both Professor 

 Warming and Fritz Muller drew the same con- 

 clusion independently, as follows : Warming 

 says: 



" Climbing plants (by stems or tendrils, etc.) 

 owe their development to the dense shade of 

 forests. 1 The young plant developed in the 

 shade appears to explain it in the following 

 manner; it is forced to grow in height, its 

 branches elongate and grow slender. The first 

 degree of evolution is presented to us by the 

 plants which simply rest upon the boughs of 

 shrubs and trees. These sarmentous plants are 

 numerous in the flora of Lagoa Santa, they 

 belong to Amarantacece, Composites, Boraginece, 

 Euphorbiacece, Violacece and even Cyperacece. 

 The adaptation is more accurately effected in 

 the branching plants, of which the branches 

 are inserted at right angles with the stem. 

 Thanks to this peculiarity, they lie easily upon 



1 He is speaking of Lagoa Santa, Brazil. 



