848 



THE POPULAR SCIENCE MONTHLY. 



at last to appear, tl;iat those who read 

 the newspapers and sustain them appre- 

 ciate matter of solid worth, and will buy 

 it and read it when it is offered to them ? 



LITERARY NOTICES. 



The Origin of Floral Structures through 

 Insect and other Agencies. By Rev. 

 George Henslow, F. L. S. Illustrated. 

 " International Scientific Scries," Vol. 

 LXIII. New York : D. Appleton & Co. 

 Pp. 349. Price, $1.75. 



This volume deals with one of the most 

 interesting departments in the whole range 

 of botanical science. It is, in fact, almost 

 common ground for both the botanist and 

 entomologist. The author accepts as a fun- 

 damental principle that environment fur- 

 nishes the influence which induces plants to 

 vary. A brief outline of the steps taken by 

 various authorities along this line, from Geof- 

 frey Saint-Hilaire in I'ZOo, to Darwin of recent 

 time and Herbert Spencer of to-day, is given 

 in the preface. 



Prof. Henslow early had his attention 

 attracted to floral structures in their relation 

 to insect visitors, and this volume is an elab- 

 orate treatise in which the object, in the au- 

 thor's own words, is to " endeavor to refer 

 every part of the structure of flowers to some 

 one or more definite causes arising from the 

 environment taken in its widest sense." The 

 early chapters deal with those elementary 

 principles so essential to a full and accurate 

 understanding of that which follows. Sym- 

 metry, or lack of it, is treated at length, and 

 many causes are assigned for the disappear- 

 ance of petals, stamens, etc., or their aug- 

 mentation. Then follows a discussion of 

 the principles of arrangement. The alter- 

 nation of the floral whorls is, for example, 

 considered due to their being composed of 

 spirals " which are projected on to the same 

 plane and so form verticils," and the posi- 

 tion of stamens follows in consequence of 

 the branching of fibro-vascular bundles. In 

 some cases the sepaline bundles give rise to 

 a whorl of stamens, and in others the petal- 

 ine cord. Why this should be is not under- 

 stood. Nutrition is the immediate cause, 

 but why the nutrition should flow in one or 

 the other direction remains obscure. 



The irritation induced by insects is a 

 potent cause of the flow of sap to certain 



parts, which encourages local growth and 

 thereby brings about a union between parts 

 of a whorl or between different whorls. 

 Prof. Henslow's theory is therefore " that 

 the forms and structures of flowers are the 

 direct outcome of the responsive power of 

 protoplasm to external stimuli." That hy- 

 pertrophy results from irritation is well shown 

 in many instances, but some persons may be 

 slow in granting all that the author is free 

 to ascribe to the theory. He, however, makes 

 a strong argument, and brings forward a great 

 array of facts. Other causes are, however, 

 not overlooked, and hereditary influences is 

 one of these. Irregularity in flowers is shown 

 to be for the purpose of securing the pollina- 

 tion of the stigma. " All flowers, as we have 

 them now, which are in perfect adaptation to 

 insect agency, are the outcome of the result- 

 ant of all the forces, external and internal, 

 which the insect has actually brought into 

 play, or stimulated into action by visiting 

 them for their honey or pollen." With this 

 working theory the author is able to show 

 good reasons for the development of flowers 

 having a bilateral symmetry. The portions 

 of a flower upon which insects alight have 

 become large and strong by responding to the 

 strain that insects have brought upon them. 

 Subsequently hereditary influences have come 

 into play, and now the enlarged part may be 

 present before there is any necessity for it. 

 At the same time compensatory degeneration 

 goes on in other parts of the flower. In the 

 tendency of irregular flowers to become regu- 

 lar under cultivation, the author recognizes 

 negative evidence to his theory. Presuming 

 that the irregularity was brought about by in- 

 sects, the demand for irregularity under cult- 

 ure being wanting, the flowers revert to their 

 ancient regular form. " Did we but know 

 what the insects were, and how they have 

 poised themselves upon the flower, and in 

 what way their proboscides and tongues have 

 irritated the different parts, one might be 

 able to describe more accurately the whole 

 process ; but that such have been the cause 

 and effect as above described, seems to me 

 to be too probable a theory to be hastily dis- 

 carded in the absence of a better one." The 

 author frequently refers to such striking ex- 

 amples of quick response in tissues to insect 

 irritation as are seen in the formation of 

 galls, and he concludes that if the stimulus 



