NATURE 



145 



THURSDAY DECEMBER 19, 1895. 



THE ORIGIN OF PLANT STRUCTURES. 

 The Origin of Plant Structures by Self-adaptation to the 

 Environment. By the Rev. G. Henslow, M;A., F.L.S., 

 t&c. International Scientific Series. Pp. xii -h 256. 

 (London: Kegan Paul, 1895.) 



THE present work may be regarded as the second part 

 of the " Origin of Floral Structures," published by 

 the same author in 1888. In that volume Prof. Henslow 

 propounded his Neo-Lamarckian view, that all differences 

 of colour, shape, and size of floral organs have been 

 directly caused by the influences surrounding the plant. 

 The visits of insects, with their constant thrusts and 

 probings, have produced, as a direct result, all the 

 variety of the phanerogam flower. 



In the present volume, the same proposition is extended 

 to the vegetative organs of plants, of which the efficient 

 cause of diversity, whether of external or internal morpho- 

 logy, is to be sought in changes in the conditions of life. 

 In this way the author makes studies of the following 

 special cases : — Desert plants, Arctic and Alpine plants, 

 maritime and saline plants, phanerogamous aquatics, 

 subterranean structures, climbing stems and leaves. From 

 a careful analysis of the biological peculiarities of these 

 forms. Prof. Henslow claims to draw strong support for 

 his views. 



The Darwinian hypothesis assumes, in the offspring, 

 constant minute variations in all directions from the 

 parent type : those variations that are of service to the 

 plant in its struggle for existence, are perpetuated and 

 increased by natural selection and heredity. Prof Hens- 

 low denies the existence of natural selection altogether : 

 variations in nature, according to him, are never in- 

 definite, but always definite, and, being induced by the 

 change of environment, and the responsive action of pro- 

 toplasm, they are always in the direction of adapting a 

 plant to its surroundings. 



The test of a theory lies in the wideness of its appli- 

 cation ; and herein exists the great beauty of Darwin's 

 hypothesis. After all these years of severest criticism, no 

 definite proofs have been urged against it ; and the best 

 that Prof Henslow can do is to offer a substitute which, 

 to his mind, furnishes an easier solution to the difficulties 

 of certain selected cases. 



Whatever may be the opinion of others, the author him- 

 self is sure of his ground. The introduction opens with 

 these words : " Natural Selection plays no part in the 

 Origin of Species." This dictum is not likely to be ac- 

 cepted by the general scientific world without very strong 

 support. The imputation of narrowness of field in 

 Darwin's observations is hardly in good taste, while such 

 headings as "Darwin's Fundamental Error" predispose 

 the mind to a critical attitude. 



It is usually agreed that, from the nature of the case, 

 a definite proof of the action of natural selection is 

 difficult, if not impossible, in the present state of our 

 knowledge. This the author of the present volume con- 

 cedes, and at the same time puts forth arguments against 

 the probability of such proofs being forthcoming. With 

 considerable skill, if with rather superfluous detail, he 

 NO. 1364, VOL. 53] 



discusses the manner in which the environment impresses 

 itself upon the anatomy of plants. Of the inheritance 

 of such acquired characters there is no proof at all. We 

 are offered instead the " argument of coincidences " and 

 the " cumulative evidence of probabilities, which amounts 

 to a moral conviction." Clearly, before rejecting a well- 

 established and widely applicable hypothesis, something 

 more tangible is required. 



In each section of the present volume, Prof. Henslow 

 presents the reader with an interesting picture of the 

 biology of a group of plants. The descriptions would, 

 we think, be clearer if the writer had condensed his 

 quotations somewhat. As it is, the interpolation in the 

 text of long passages — frequently in French — mars the 

 simplicity. 



We emphasise this point because of the character of 

 the author's reasoning. He is an exceedingly plausible 

 and persevering casuist ; and it is, on that account, all 

 the more desirable that the reader should retain a clear 

 impression of the course of the argument. 



To take a specimen of the author's method. In speaking 

 of the frequent hairiness of desert plants, as contrasted 

 with those more favourably situated, Prof. Henslow 

 quotes Mer, to the effect that " cceteris paribus hairs 

 are the result of localised extra nourishment." This, he 

 points out, was long ago suggested by Aug. Pyr. de 

 Candolle as the cause of the hairiness of the barren 

 inflorescence of Rhus Cotinus, where the nutrition, 

 which would normally be applied to the formation of 

 flowers and seeds, finds a new outlet. So with the hairy 

 filaments of Verbascuni and other flowers where some 

 of the anthers are barren or suppressed ; also, as 

 Masters has pointed out, the hairy outgrowths in many 

 galls. 



The " localised extra nourishment " of desert plants 

 the author accounts for in the following manner. There 

 is a characteristic diminution in the size of the leaves in 

 desert plants, due principally to a decrease in the paren- 

 chymatous tissues ; hence, it is argued, there is an 

 arrested food supply which, " by a compensating process,'' 

 is used up in the formation of hairs. 



To take another instance : the rapid maturing and 

 seeding of plants, in regions of short summer, is traced 

 to the changes which take place in the reserve materials 

 during the low temperatures of the long winter pre- 

 ceding, just as frosted potatoes shoot out quickly in the 

 spring. 



We are not sure that, in these attempts to define the 

 exact mode of "the responsive action of protoplasm," 

 the author does not deprive it of more of its independent 

 and unexplained reactions than is justified by our present 

 knowledge. 



In a word, each argument, although composed of a 

 chain of neat and plausible propositions, lacks coherence 

 and, somehow, fails to carry conviction. In each change 

 of environment, the protoplasm is, so to speak, induced, 

 by a kind of internal conjuring, to present the very 

 modificatio'n of structure which will be of service to the 

 plant under the altered conditions. 



It has been pointed out that only isolated cases have 

 been dealt with in this volume ; but, for the hypothesis 

 to be acceptable, it must be widely applicable. We 

 should like to learn how the beautifully fashioned hooks 



H 



