Chap. XXIII. CONDITIONS OF LIFE. 281 



It would be travelling beyond my proper limits here to discuss how far 

 organic beings in a state of nature are definitely modified by changed con- 

 ditions. In my ' Origin of Species' I have given a brief abstract of the 

 facts bearing on this point, and have shown the influence of light on the 

 colours of birds, and of residence near the sea on the lurid tints of insects, 

 and on the succulency of plants. Mr. Herbert Spencer 45 has recently dis- 

 cussed with much ability this whole subject on broad and general grounds. 

 He argues, for instance, that with all animals the external and internal 

 tissues are differently acted on by the surrounding conditions, and they 

 invariably differ in intimate structure. So again the upper and lower sur- 

 faces of true leaves, as well as of stems and petioles, when these assume the 

 function and occupy the position of leaves, are differently circumstanced 

 with respect to light, &c, and apparently in consequence differ in struc- 

 ture. But, as Mr. Herbert Spencer admits, it is most difficult in all such 

 cases to distinguish between the effects of the definite action of physical 

 conditions and the accumulation through natural selection of inherited 

 variations which are serviceable to the organism, and which have arisen 

 independently of the definite action of these conditions. 



Although we are not here concerned with organic beings in 

 a state of nature, yet I may call attention to one case. Mr. 

 Meehan, 46 in a remarkable paper, compares twenty-nine kinds of 

 American trees, belonging to various orders, with their nearest 

 European allies, all grown in close proximity in the same garden 

 and under as nearly as possible the same conditions. In the 

 American species Mr. Meehan finds, with the rarest exceptions, 

 that the leaves fall earlier in the season, and assume before 

 falling a brighter tint; that they are less deeply toothed or 

 serrated ; that the buds are smaller ; that the trees are more 

 diffuse in growth and have fewer branchlets ; and, lastly, that 

 the seeds are smaller— all in comparison with the corresponding 

 European species. Now, considering that these trees belong to 

 distinct orders, it is out of the question that the peculiarities 

 just specified should have been inherited in the one continent 

 from one progenitor, and in the other from another progenitor; 

 and considering that the trees inhabit widely different stations, 

 these peculiarities can hardly be supposed to be of any special 



of food on caterpillars, see a curious ii. 1866. The present chapters were 



account by M. Michely, in 'Bull.de la written before I had read Mr. Her- 



Soc. Imp. d Acchmat.,' torn. viii. p. 563. bert Spencer's work, so that I Lave not 



For analogous facts from Dahlbom on been able to make so much use of it 



Hymenoptera, see Westwood's ' Modern as I should otherwise probably have 



Class, of Insects,' vol. ii. p. 98. See also done. 



Dr. L. Moller, 'Die Abhangigkeit dor 46 <p roo AcacL Nai SoC- of PMla _ 



Insecten/ 1867, s. 70. delphia,' Jan. 28th, 1862. 

 45 ' The Principles of Biology,' vol. 



