Oct. 14, 1875J 



NATURE 



513 



absolutely new, are worth recording, and should be well 

 known to forest officers. Thus we are told (page 278) the 

 proportion of water contained in wood varies according 

 to the season. Schubler and Neuffler found in the fir 

 (Abies) 53 per cent, in January and 61 in April ; in the 

 ash {Fraxitnis), 29 per cent, in January and 39 in April. 

 These facts prove that trees contain more water at the 

 time of the ascent of the sap than in winter. Besides, 

 it has been found that small branches contain more free 

 water than large ones, and that these last contain more 

 than the trunk, which results agree with the knowledge 

 we possess of the porous nature of the different parts. 

 The presence of the bark retards desiccation consider- 

 ably. 



Uhr having had some trees felled in June, after the 

 ascent of the sap, and then having had them placed in 

 the shade, found that those from which the bark had been 

 removed had lost 3453 per cent, of water in July, 3877 in 

 August, 39'34 in September, 32*62 in October ; whilst 

 those with the bark untouched had only lost during the 

 same periods 0*41, o"84, o"92,o"98. Thus it will be seen 

 that the desiccation of barked wood proceeds much more 

 rapidly. It is only stripped trunks of small size and soft 

 wood that dry up with the rapidity above mentioned. 



The numerous woodcuts dispersed throughout the book, 

 and more especially those showing the defects of wood, 

 are accurate representations of the subjects intended to be 

 illustrated. A large portion of the book is devoted to the 

 consideration of felling and cutting up timber, and of 

 machinery used in its manipulation. J. R. J. 



OUR BOOK SHELF 



Zur lehre der Parallel-projection vnd der Flcichen. Von 



Prof. Dr. Wilhelm Matzka. (Prag, 1874.) 

 Gruiidziii^e ciner Theorie der cubischen Involutionen. 



Von Dr. Emil Weyr. (Prag, 1874.) 

 These two reprints from the " Abhandlungen der k. 

 bohm. Gesellschaft der Wissenschaften " are purely ma- 

 thematical, as may be gathered from their titles. The 

 author of the first treatise states that the orthogonal pro- 

 jection of broken hnes on given axes, whether in a plane 

 or in space, has been discussed in scientific works on 

 theoretical and practical mathematics, but the obliqtie 

 projection has not obtained so great prominence. The 

 subject is gone into very thoroughly by Dr. Matzka, as 

 may be inferred from the fact of its discussion occupying 

 70 quarto pages. 



The work by Dr. Weyr needs only to be mentioned in 

 these columns, as his exhaustive treatment of any subject 

 he takes in hand, especially of a geometrical character, is 

 ■well known — " Nihil tetigit, quod non ornavit." The 

 treatise occupies 54 quarto pages. 



Practical Hints on the Selection and Use of the Micro- 

 scope. By John Phin. (The Industrial Publication 

 Company, New York.) 



The contents of the small volume before us fully justify 

 the wording of its title. On the other side of the 

 Atlantic the system of puffing worthless optical instru- 

 ments seems to be on a much greater scale than in this 

 country. " To the young student whose means are 

 limited, and to the country practitioner whose ability to 

 supply himself with instruments often falls far short of 

 his desires, the offer of a serviceable microscope for a 

 couple of dollars is a great temptation, and when the 

 instrument in question is endorsed by a long list of 

 clergymen, lawyers, and even editors, this temptation 



becomes irresistible." To show what these worthless 

 microscopes really are, and what ought to be expected of 

 the most ordinary one, are the main objects the author 

 has in view in the earlier pages of the work. Further on 

 he explains the manner of using the instrument, and 

 the method of mounting specimens for examination. 

 Accurate formulae are given for the preparation of a large 

 number of preservative solutions, amongst which we do 

 not find any sufficiently novel to deserve special mention. 

 It is in the practical nature of its remarks, and not in 

 their novelty, that the value of Mr. Phin's short book 

 rests, and to the tyro it will be found to give information 

 of real value. Beside Mr. R. B. Tolles, J. Grunow, J. 

 Zentmayer, and W. Wales are mentioned as manufac- 

 turers of good objectives in the United States ; and Mr. 

 McAllister's stands are particularly praised. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the ivriters of, rejected manuscripts. 

 No notice is taken of anonymous communications.'^ 



The Sleep of Flowers 

 In your " Notes " (vol. xii. p. 484) you mention a recent paper 

 by M. Royer on this little-understood class of phenomena. We are 

 acquainted with the objects of most of the spontaneous and periodi- 

 cal movements of plants, but of the physiological means by which 

 these same movements are effected we know little or nothing. But 

 it is important to remember that phenomena like in effect may be 

 diverse in cause. The folding up of petals may have nothing 

 physiologically in common with that of foliage-leaves. In fact, 

 these phenomena may be divided into several classes. Thus 

 movements due to irritation or concussion must be considered 

 apart from those due to spontaneity, and the movements which 

 form part of the series of processes of growth, such as the first 

 unfolding of leaves and flowers, from those which occur in 

 mature organs, though movements belonging to any two of these 

 classes may be exhibited by the same plant, as in Oxalis and 

 Mimosa. Cerens grandijlorus opens between 7 and 8 p.m., 

 Mtrabilis jalapa between 5 and 7 P.M. There is every proba- 

 bility that these times are those at which the insects which fer- 

 tilise these two species also come forth, and that the same object 

 exists in the case of other species which open and close 

 their flowers more than once, "waking" and "sleeping;" 

 but in the case of Cereus and Mirabilis the movement is one of 

 growth only, though, no doubt, affected by external influences, 

 such as the variation of heat and light. We have, however, 

 cases of true ' ' sleep " in Ipomaa nil and Calystegia sepium, which 

 open between 3 and 4 a.m. ; Tragopogon, the ligulate florets of 

 which behave like petals, and which, opening at the same time, 

 closes again before noon ; Anagallis arvensis, opening at 8 A.M. 

 and closing when the sky is overcast ; the Mesembryanthaceoe, 

 which open generally about 12 — Mesembryanthemum nccti- 

 florum, which opens between 7 and 8 p.m., being an excep- 

 tion ; and Victoria regia, which opens for the first time about 

 6 P. M. , closes in a few hours, opens again at 6 A. m, , and closes 

 finally and sinks in the afternoon ; and in many other cases. 

 Besides the causes mentioned in your note, the movements have 

 been attributed to actinism. That they are not hygrometric is 

 clear from the fact stated by Sachs, on the authority of unpub- 

 lished experiments by Pfeffer (" Text-book of Botany," p. 798), 

 that they take place under water. These same experiments 

 show them to be due to variations in the temperature, and when 

 the temperature is constant, to variations in the intensity of 

 light, and also to be accompanied, at least in some cases, with an 

 increase of the length of the inner side of the phyllre of the 

 perianth when opening. Light certainly seems to have more to 

 do with the movements of the "poor man's weather-glass" than 

 heat, though perhaps atmospheric pressure might equally well be 

 argued to be their cause. We must remember that as osmotic 

 action is constantly going on at the root-hairs and in the grow- 

 ing parts of living plants, so a constant molecular diflusion of 

 gjSes is going on through cell-walls, besides the passage of gases 

 through stomata. " The movements of diflusion," as Sachs 

 says (p. 614), "tend to bring about conditions of equilibrium 

 which depend on the co-efScients of absorption of the gas by 



