Remarks on the Nature and Definition of Species. 53 



ib moved as a whole without generation of heat. Apply the 

 same force at a blow and the energy is resolved into molecular 

 \'ibrations, mavbe even disruptively, \\ith much internal heat 

 and no motion as a whole. 



In extreme cases acclimatization may affect even the \-isible 

 structure, particularly in organisms \\ith many delicately corre- 

 lated parts. Changes of this sort have been very generally 

 ignored in the post-Darwinian discussion of evolution, because 

 it is said, rightly enough in all probability, that none of them 

 are permanent. By this is intended that if the organism or its 

 offspring be removed to the old habitat the old form \\aLl re- 

 appear. Xaturallv; what else is to be expected in a plastic 

 organism? But surelv the fact merits serious consideration that 

 so long as the plant endures the new conditions so long will its 

 new facies remain constant ; while in its offspring, each genera- 

 tion, if it does not suffer any mutation, may respond in the 

 same fashion— so long as it remains under the same con- 

 ditions. If then, the organism were to die out in its original 

 habitat (as is happening for example to Cupressus macrocarpa, 

 which has been carried to endless new habitats in cultivation) 

 what would be left to distinguish our "ecad" from a species? 

 All that we should know about it is what we know about any 

 species, that in its normal habitat it had one form, observably 

 constant under constant conditions, and that when moved it 

 showed a liabilitv to displav other, apparenth' latent capabilities 

 of development. 



True, to go back to the beginning again, during the first few 

 generations under the new conditions the new character might 

 be, to an observer, ob\-iously superposed during development 

 on an originally different habit, manifested in the juveniles. 

 But the h\-ing organism is not restricted to the passi\'ity of 

 our strained metallic wire. A fruit stalk thickens as the 

 weight upon it grows heaw, a \\ire cannot. The plant has a 

 plastic organization, governed by that mysterious process called 

 "facilitation by repetition," mysterious in its cause but plainly 

 manifest in its effects; through the operation of which we find 

 the new characters of our ecad appearing earlier and earlier 

 in each successive generation until they may even eventually 

 show themselves in the embryo. The change-over is complete, 

 our "ecad" has become a "species." 



This fascinating idea, closely boimd up ^^ith the phenomenon 

 of embrvonic recapitulation, is too big a matter to enter into 

 here in the detail which its importance to the theory of plant 

 evolution deserves; but this simple sketch of the principles 

 involved will help to emphasize the \iew here taken, that the 

 organism is a crystallized habit. Permanence, as applied to 



