178 NATURAL SCIENCE. Sept.. 



adducing some adequate and proved substitute. What Mr. Henslow 

 does put in its place is the reaction of vegetable tissues to the environ- 

 ment, resulting in adaptation ; and in the special case of ilowers he 

 imputes all the variety of form and endless modifications of structure 

 to " the responsive action of the protoplasm, in consequence of the 

 irritations set up by the weights, pressures, thrusts, tensions, etc., 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 interesting 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 he quotes Darwin as saying that the 

 excellence of our milking cows and goats may be attributed partly to 

 selection and ^* partly to the inherited effect of the increased action, through 

 man's art, of the secreting glands," and adds, " This fact " is strictly 

 analogous to what takes place in the vegetable kingdom ! Here we have 

 a mere opinion of Darwin's, nowhere supported by direct observation 

 or experiment, and now seriously challenged by a large body of 

 naturalists, set forth as " a fact." Again, at page 157, the case of 

 the various "ant-plants" of the eastern tropics is referred to, and it 

 is stated that Dr. Beccari explains the curious hollow stem in which 

 the ants dwell as partly due to the irritation of the ants inducing 

 hypertrophy of the vegetable tissue, which " then becomes hereditary" ; 

 and Mr. Henslow concludes that there is abundant evidence to prove 

 that many organs of a plant, if subjected to irritation, can become 

 materially altered and develop new processes, and, "secondly, that 

 these altered states, if the irritation be persisted in, may becom.e 

 hereditary." Here again are only opinions without a particle of 

 proof; and I can find nothing more to the point in the whole 

 volume. The case of galls is very briefly referred to at p. 144, and 

 their non-heredity is passed by with the remark that the predisposition 

 to produce them may be greater now than formerly, and that the 

 galls themselves may be larger than they were at first. But surely 

 if the effects of insect irritation are anywhere hereditary it would be 

 here. An oak tree which lives several hundred years is subject to 

 this irritation in greater or less degree almost every year, and the 

 irritation itself is not momentary and intermittent, as in the case of 

 insects visiting flowers, but is kept up by the presence of the egg and 

 growing larva during a considerable portion of the period of active 

 vegetable growth, and this has been going on for thousands, probably 

 millions, of years. Yet neither do oaks nor any other plants produce 

 galls spontaneously, as they certainly should do if the results of 

 irritations are in any general sense hereditary. This seems to me 

 to be a really crucial experiment continually repeated by nature. 



I may here remark that Mr. Henslow's theory utterly breaks 

 down owing to the want of any conceivable connection between 

 1 "The Origin of Floral Structures," p. 340. 



