32 PROOFS OF HEREDITY [CHAP. 



ditions of the environment ; and although they 

 may at once begin to change if the environment 

 is changed, the original tissues last long enough 

 to prove that they have been acquired and are 

 hereditary, since they are reproduced when the 

 trees are raised from seed in a totally different 

 locality and environment, as the Araucaria in 

 England, and the water crowfoot in a garden. 



As it is with timber so is it with the stems 

 and woody shrublets. There are many spiny 

 xerophytes, the spines may be abortive or arrested 

 branches as of the sloe, hardened like the wood 

 described above, or they may be spinescent leaves 

 as in the barberry ; or both branches and leaves, 

 as in the furze. On growing any such plant in 

 moist air and soil, the inevitable result is the 

 gradual disappearance of the spines and spiny 

 leaves, and the corresponding elongation into 

 branches bearing fully- developed leaves. 



The following is an experiment I made with 

 the common rest - harrow (Ononis spinosa, L., 

 fig. 3), growing wild in a very dry situation 

 by a roadside. I collected some seeds, and also 

 took cuttings. These I planted in a garden 

 border, keeping this well moist with a hand 

 light over it, and a saucer of water so that the 

 air should be thoroughly moist as well. Its 

 natural conditions were thus completely reversed. 

 They all grew vigorously. The new branches 

 of the first year's growth bore spines, proving 



