372 



SCIENCE. 



[N. S. Vol. VIII. No. 194. 



be produced as readily as the illusions con- 

 nected with a square within a square. A cer- 

 tain distance for a point of observation and also 

 a certain speed of rotation appears to be neces- 

 sary, for fans nearer the observer rotating more 

 slowly do not produce the phenomenon which 

 now seems to be due to the same principle of 

 accommodation that makes a figure of a square 

 within a square appear at one time as a hollow 

 space and at another as a solid. 



Two other illusions connected with the fan, 

 but which may be well known to every one who 

 has watched moving machinery, may be noted. 

 In one the vanes, instead of rotating, seem to 

 flap together ; in the other the two iron arms 

 appear to be continually withdrawing into and 

 pushing out from the hanging rod. 



F. C. Kenyon. 



SCIENTIFIC LITERATURE. 

 Plant Life, Considered with Reference to Form 

 and Function. By Chakles Reid Barnes, 

 Professor of Plant Physiology in the Univer- 

 sity of Chicago. New York, Henry Holt & 

 Co. 1898. 12mo. Pp. x + 428. 

 In his preface the author says: "The ab- 

 sence of an elementary accouut of the form and 

 functions of the plants of all groups has made 

 itself felt," and "I am not aware that any book 

 at present attempts to meet this need." These 

 sentences, coupled with the author's reference 

 to secondary schools, and to pupils of thirteen 

 to eighteen years of age, indicate the purpose 

 and place of the book. 



In carrying out his plan he has divided the 

 subject into four parts, viz. : (1) the vegetative 

 body; (2) physiology ; (3) reproduction, and (4) 

 ecology. In the first part appear such chapter 

 headings as 'the unit of structure,' 'single- 

 celled plants and colonies,' ' linear and super- 

 ficial aggregates,' 'the thallus of the higher 

 algse,' the fungus, body of hyphal elements,' 

 ' liverworts and mosses,' ' fernworts and seed- 

 plants.' A few years ago such an approach to 

 what was then called ' morphology ' would 

 have horrified the old-time teachers of ele- 

 mentary botany, who were anxious to give the 

 study as much 'practical ' value as possible, and 

 were wont to repeat pedagogical platitudes as 

 to the necessity of ' proceeding from the known 



to the unknown.' Ignoring such objections, 

 the author leads the pupil, chapter by chapter, 

 from the relatively simple plant-body of the 

 fission algse to the highly complex structures, 

 roots, stems and leaves, of the seed plants. The 

 significance of the latter is thus made much 

 clearer than by the old method of studying the 

 anatomy of flowering plants first, and then fol- 

 lowing with something of the lower forms from 

 which they sprang. 



The treatment of the physiology of plants is 

 satisfactory, as a matter of course, since the 

 author has given especial attention to this de- 

 partment of botany. In the introduction some 

 clear and useful definitions are given ; then fol- 

 lows a suggestive chapter on the maintenance 

 of bodily form, one on nutrition (particularly 

 well done), one on growth and another on the 

 movements of plants. 



The chapters relating to reproduction must 

 be very helpful in giving the beginner right no- 

 tions as to how plants provide for a succession 

 of individuals. Old-fashioned people will open 

 their eyes when they find the ' flower ' dis- 

 cussed in the chapter treating of vegetative 

 (i.e., asexual) reproduction, along with 'fis- 

 sion,' 'budding,' 'spores' and 'brood buds.' 

 The ' flower ' is brought in under the general 

 topic ' spores,' after the discussion has led up to 

 the differentiation of spores into megaspores 

 and microspores. Of course, this is all right, 

 as everj' botanist knows, but there will be some 

 scrambling and tumbling on the part of many a 

 high-school teacher as he attempts to lead his 

 pupils through this, to him very new, territory, 

 and we imagine that he will fare little better 

 when he comes to the angiosperms in the chap- 

 ter on sexual reproduction. In order fully to 

 master this matter the teacher will, in most 

 cases, be obliged to spend a term or two in some 

 good botanical laboratory, where he can be 

 helped over the difficult places. 



The chapters on ecology are new to American 

 books on botany, and while they are quite ele- 

 mentary they will be useful in the way of di- 

 recting students and teachers into a compara- 

 tively new field of work. 



The appendices are in some respects of more 

 value than the body of the book, giving as they 

 do : (1) directions for laboratory study ; (2) direc- 



