April 6,, 1878] 



JVATlfRE 



445 



loss how to come at the truth of the current temperature 

 of this climate as the thermometrical observations which 

 are now regularly published in the Philosophical Transac- 

 tions can furnish us with a proper standard with which 

 the solar phenomena may be compared. This leads me 

 to remark that although I have in my first paper suffi- 

 ciently noticed the want of proper criterion for ascer- 

 taining the temperature of the early periods where the 

 sun has been recorded to have been without spots, and 

 have also referred to future observations for showing 

 whether a due distribution of dry and wet weather with 

 other circumstances which are known to favour the 

 vegetation of corn, do or do not require a certain regular 

 emission of the solar beams, yet I might still have added 

 that the actual object we have in view is perfectly inde- 

 pendent of the result of any observations that may here- 

 after be made on ihe favourable or defective vegetation of 

 grain in this or in any other climate .... It may be 

 hoped that some advantage miy be derived even in 

 agricultural economy, from an improved knowledge of 

 the nature of the sun and of the causes or symptoms of 

 its emitting light or heat more or less copiously." 



It perhaps will be news to many that the idea of a 

 possible connecttion between sun-spots and rainfall 

 which has been represented as a modern idea, may really 

 be credited to a man whose chief work was done in the 

 last century. 



DARWIN'S ''DIFFERENT FORMS OF 

 FLOWERS" 



The Different Forms of Flowers on Plants of the same 

 Species. By Charles Darwin, M.A., F.R.S. (London: 

 John Murray, 1877.) 



THIS is another of the remarkable series of volumes 

 in which Mr. Darwin has given us the extremely 

 valuable results of his researches in the vegetable side of 

 biology. Mr. Darwin's method of investigation would 

 in itself be a very interesting subject for consideration. 

 It is, however, sufficient to point out that its characteristic 

 feature is the combined attack upon a given problem 

 from both its morphological and physiological aspects. 

 This method Mr. Darwin employs with consummate suc- 

 cess, and in turning over the pages of the present book — 

 a considerable part of which has been before the world 

 for more than a decade without being materially im- 

 pugned—one is almost distracted from the intrinsic in- 

 terest of the facts and speculations by the sagacity with 

 •which the research is carried on, and the skill with which 

 the results are marshalled for our information. It is 

 peculiarly worthy of notice in the present volume how the 

 reader is allowed, in studying Mr. Darwin's pages, to form 

 his own hypotheses in explanation of the facts, only to be 

 compelled in due course, as the narrative proceeds, to 

 admit that such hypotheses are utterly untenable. There 

 is no impression so curious as to find oneself so distinctly 

 under the hands of a master, and to realise that the calm 

 flow of the argument proceeds over the debris of objec- 

 tions and difficulties which are found to be already com- 

 minuted as soon as one attempts to give them any definite 

 form. 



It would be quite impossible to treat, in the short space 

 at our disposal, all that calls for notice in the present 

 volume. Commencing with a short introduction, the 

 body of the book falls into three divisions. The first 

 treats of heterostyled plants, and contains in a connected 

 form the substance of Mr. Darwin's various papers com- 



municated to the Linnean Society. The second and 

 third divisions are much shorter, and treat respectively of 

 the passage of hermaphrodite into dioecious plants, and of 

 cleistogamic flowers. 



As has been already remarked, Mr. Darwin's researches 

 on what are now termed heterostyled plants' have been 

 common scientific property for many years, and have 

 filtered down into the current text-books. The seventh 

 and eighth chapters are therefore the essentially new part 

 of the book, and these we shall more particularly con- 

 sider. 



The vast majority of flowering plants are, as is well 

 known, hermaphrodite, that is to say, they contain within 

 the same floral envelopes both male and female organs- 

 The governing principle in the morphological adaptations 

 of flowers is apparently to escape the obvious consequences 

 of such juxtaposition and evade seU- fertilisation. This is 

 effected either by theirbeingdichogamic — that is the sexual 

 organs in any one flower maturing at different times, or 

 by their being entomophilous — that is calling in the inter- 

 vention of insects to carry the pollen of one flower to the 

 stigma of another, or by their being heterostyled — that is 

 by the flower bein^ modified in two or three ways, 

 admitting of a certain number of reciprocal modes of 

 fertilisation which are legitimate, and of others which are 

 distinguished as illegitimate, and are more or less sterile. 



Each of these modes of avoiding self-fertilisation prac- 

 tically sets up a functional separation of the sexes, and it 

 might seem that the cases in which this separation is 

 structurally accomplished are its natural sequence. Mr. 

 Darwin points out, however, very conclusively that this 

 is by no means the case. 



" There is much difficulty in understanding why her- 

 maphrodite plants should ever have been rendered 

 dioecious. There would be no such conversion unless 

 pollen was already carried regularly by insects or by the 

 wind from one individual to the other, for otherwise every 

 step towards dioeciousness would lead towards sterility. 

 As we must assume that cross-fertilisation was assured 

 before an hermaphrodite could be changed into a dioe- 

 cious plant, we may conclude that the conversion has not 

 been effected for the sake of gaining the great benefits 

 which follow from cross-fertilisation." 



Mr. Darwin is led to find an explanation in the advan- 

 tage to the plant in the diminished strain of producing 

 sexual organs of only one kind instead of both. And 

 the process of manufacturing dioecious plants is one 

 which can be actually seen in process. The cultivated 

 strawberry under the influence of the American climate 

 is a marked instance. In such cases the hermaphrodite 

 state can be traced into the dioecious with every inter- 

 mediate grade. The ultimate fate of heterostyled plants 

 is perhaps to be converted into dioecious ones, and in this 

 instance the change would be more immediate and with 

 fewer connecting links. The functional diversity already 

 exists and the corresponding suppression of the sexual 

 organs is all that is needed to render it complete. 



The concluding chapter on cleistogamic flowers cer- 

 tainly does not yield in interest to any preceding portion 

 of the book. The existence of these curiously-modified 

 structures has long been known, but it is only within the 

 last twenty years that they have been attentively studied, 

 and Mr. Darwin's account.is a very masterly discussion of 

 all that has been written on a very puzzling subject, tested 



