iv.] EXPERIMENTAL PROOFS 31 



in its native mountain sides. The tree is raised 

 from seed, and much grown in England. I had 

 occasion to cut an old tree down, and the man 

 found that he was unable to saw it through, just 

 as Mr Reid describes the Kauri pine, and so 

 chopped it down with an axe. 



This hardness is solely due to drought. M. 

 Ph. Eberhart 1 experimented with many kinds 

 of woody stems, growing them in ordinary air, 

 very moist conditions and a very dry one, 

 respectively. The results were most marked, 

 all the " mechanical tissues " such as wood 

 being strongly developed, as well as "scleren- 

 chyma " of the bast ; whereas, all such tissues 

 at once failed to be well developed under the 

 second, as compared with stems grown normally 

 under the first (fig. 2). He thus proved by 

 experimental verification the general truth of 

 the inference which Mr Reid drew from the 

 Kauri pine alone. 



If we take the Kauri pine and the Araucaria 

 as extreme types of xerophytic trees, and com- 

 pare the structure of their stems, first with 

 mesophytes, and then with hydrophytes, we 

 see at once how wood and other mechanical 

 tissues decrease until, in a submerged stem 

 they are almost entirely wanting. The infer- 

 ence is irresistible that the structure of the 

 stem is in response to climatal and other con- 



1 Ann. des Sci. Nat., torn, xviii., p. 61, 1903. 



