Chap. XXIII. CONDITIONS OF LIFE. 275 



remark to show how profoundly, yet in how natural a manner, this 

 plant, must have been modified by the parasitic fungus. Mr. 

 Meehan 66 also states that three species of Euphorbia and Portulaca 

 olereacea, which naturally grow prostrate, become erect when they 

 are attacked by the QScidium. Euphorbia maculata in this case also 

 becomes nodose, with the branchlets comparatively smooth and the 

 leaves modified in shape, approaching in these respects to a distinct 

 species, namely, the M. hypericifolia. 



Facts and Considerations opposed to the belief that the Conditions 

 of Life act in a potent manner in causing definite Modifications 

 of Structure. 



I have alluded to the slight differences in species naturally 

 living in distinct countries under different conditions ; and 

 such differences we feel at first inclined to attribute, probably 

 often with justice, to the definite action of the surrounding con- 

 ditions. But it must be borne in mind that there exist many 

 animals and plants which range widely and have been exposed 

 to great diversities of climate, yet remain uniform in character. 

 Some authors, as previously remarked, account for the varie- 

 ties of our culinary and agricultural plants by the definite 

 action of the conditions to which they have been exposed in 

 the different parts of Great Britain ; but there are about 200 

 plants 57 which are found in every single English county ; and 

 these plants must have been exposed for an immense period 

 to considerable differences of climate and soil, yet do not 

 differ. So, again, some animals and plants range over a large 

 portion of the world, yet retain the same character. 



Notwithstanding the facts previously given on the occurrence of 

 highly peculiar local diseases and on the strange modifications of 

 structure in plants caused by the inoculated poison of insects, and 

 other analogous cases; still there are a multitude of variations — 

 such as the modified skull of the niata ox and bulldog, the long 

 horns of Caffre cattle, the conjoined toes of the solid-hoofed swine, 

 the immense crest and protuberant skull of Polish fowls, the crop 

 of the pouter-pigeon, and a host of other such cases — which we can 

 hardly attribute to the definite action, in the sense before specified, 

 of the external conditions of life. No doubt in every case there 

 must have been some exciting cause ; but as we see innumerable 



50 ' Proc. Acad. Nat. Sc, Philadel- « Hewett C. Watson, ' Cybele 



phia,' June 10, 1874, and July 23, Britannica,' vol. i., 1847, p. 11. 

 1875. 



T 2 



