II] OF THE HEIGHT OF A TREE 29 



or stunted appearance of old and large ones*. In short, as Goethe 

 says in Dicktung und Wahrheit, "Es ist dafiir gesorgt dass die Baume 

 nicht in den Himmel wachsen." 



But the tapering pine-tree is but a special case of a wider problem. 

 The oak does not grow so tall as the pine-tree, but it carries a heavier 

 load, and its boll, broad-based upon its spreading roots, shews a 

 different contour. Smeaton took it for the pattern of his Hghthouse, 

 and Eiffel built his great tree of steel, a thousand feet high, to a 

 similar but a stricter plan. Here the profile of tower or tree follows, 

 or tends to follow, a logarithmic curve, giving equal strength 

 throughout, according to a principle which we shall have occasion 

 to discuss later on, when we come to treat of form and mechanical 

 efficiency in the skeletons of animals. In the tree, moreover, 

 anchoring roots form powerful wind-struts, and are most de- 

 veloped opposite to the direction of the prevailing winds; for the 

 lifetime of a tree is affected by the frequency of storms, and its 

 strength is related to the wind-pressure which it must needs with- 

 standf. 



Among animals we see, without the help of mathematics or of 

 physics, how small birds and beasts are quick and agile, how slower 

 and sedater movements come with larger size, and how exaggerated 

 bulk brings with it a certain clumsiness, a certain inefficiency, an 

 element of risk and hazard, a preponderance of disadvantage. The 

 case was well put by Owen, in a passage which has an interest of 

 its own as a premonition, somewhat Hke De. Candolle's, of the 

 "struggle for existence." Owen wrote as follows J: " In proportion 

 to the bulk of a species is the difficulty of the contest which, as a 

 living organised whole, the individual of each species has to maintain 

 against the surrounding agencies that are ever tending to dissolve 

 the vital bond, and subjugate the Hving matter to the ordinary 

 chemical and physical forces. Any changes, therefore, in such 

 external conditions as a species may have been original|y adapted 



* The stem of the giant bamboo may attain a height of 60 metres while not more 

 than about 40 cm. in diameter near its base, which dimensions fall not far short 

 of the theoretical limits; A. J. Ewart, Phil. Trans, cxcviii, p. 71, 1906. 



t Cf. {int. al.) T. Fetch, On buttress tree-roots, Ann. R. Bot. Garden, Peradenyia, 

 XI, pp. 277-285, 1930. Also au interesting paper by James Macdonald, on The 

 form of coniferous trees. Forestry, vi, 1 and 2, 1931/2. 



X Trans. Zool. Soc. iv, p. 27, 1850. 



