306 STUDIES, SCIENTIFIC AND SOCIAL 



the fifteen different modes of variation observed by Alph. 

 de Candolle on a single oak tree, while in a great number 

 of common species an equal amount of variability may be 

 observed both in wild and cultivated individuals ; and all 

 these variations are indefinite, in the sense that they do 

 not usually occur in one direction only, from the typical 

 form. A few examples of such variations have been given 

 in my Darwinism, pp. 76 — 80. I cannot, therefore, 

 understand either the meaning or the value of the state- 

 ment — " natural variation is alivays definite.'' 



It is not quite clear whether Mr. Henslow admits the 

 agency of Natural Selection at all. He says : " I would 

 ask what/c/ci^s are producible to prove that Natural Selec- 

 tion acts at all on the maintenance, if not the origin, of 

 any floral and, indeed, other structures ? " It is, of course, 

 admitted that direct proof of the action of Natural Selec- 

 tion is at present wanting ; but the indirect proofs have 

 been so cogent as to overcome the most violent prejudice 

 and opposition, and to convert a large majority of natu- 

 ralists to a belief in its agency. It is, therefore, rather 

 lale in the day to deny its existence without adducing 

 some adequate and proved substitute. 



Mr. Hensloius Theory. 



Mr. Henslow's contention is that the reaction of vege- 

 table tissues to the environment, is the direct cause of 

 adaptation ; and in the special case of flowers he imputes 

 all the variety of form and endless modifications of struc- 

 ture to " the responsive action of the protoplasm, in 

 consequence of the irritations set up by the weights, 

 pressures, thrusts, tensions, &c., of the insect visitors." ^ 

 Now the very first essential to this theory is to prove that 

 modifications produced by such irritations are hereditary. 

 Here, if anywhere, we want facts. Yet in the very inter- 

 esting volume to which Mr. Henslow refers us, crowded 

 as it is with facts and observations, I can find only two or 

 three slight references to this most vital point. At page 

 147 of the same volume, he quotes Darwin as saying that 

 ^ Tht Oriijin of Floral Structures, p. 340. 



