March i, 1877] 



NATURE 



373 



improved form, which gives a field nearly if not quite as 

 large as that of the instrument of Norremberg and some- 

 what better definition near the edges ; and, by the use of 

 a scale engraved on a glass plate, approximate measure- 

 ments of the angle of the optic axes of a crystal can be 

 obtained when the apparent angle is not too great for the 

 optic axes, or rather the " eyes" of the axes to be seen in 

 the field of the instrument. 



The application of the principle of von Kob^ll's 

 stauroscope, enhanced in its sensitiveness by the use of 

 the ingenious doubled calcite plate of Brezina, is also 

 valuable for ensuring precision in determining the direc- 

 tions of the principal sections of a crystal, and is for 

 example far more commodious than Descloizeaux's 

 method of dividing a plate of an oblique crystal, cut 

 parallel to the plane of symmetry, into two, and turning 

 them after the manner of an artificial twin. 



The crystallographic portion of Prof. Groth's work is 

 good, especially so from the point of view of the student in 

 the German universities, where the honoured name of 

 Naumann still holds crystallographers by the spell of a 

 notation which has the advantage of looking very simple, 

 while in reality it is complex and incomplete, and for 

 purposes of calculation, and indeed for other than a very 

 superficial crystallographic representation of crystal forms 

 — not of crystal faces — has next to no value. 



Of course. Prof. Groth is too sound and excellent a crys- 

 tallographer not to feel and to acknowledge as he does in 

 his preface, the great superiority of the method of Prof. 

 Miller for all the purposes which give crystallography its 

 character as a science ; and accordingly he introduces his 

 readers to the system of Miller, co-ordinating the two 

 methods of notation in his descriptions of crystalline forms. 

 Indeed, when he touches on the fundamental principles 

 of crystallography in his section on the doctrine of zones, 

 he discards at once the notation of his illustrious country- 

 man, and handles the subject entirely in the language and 

 method of Miller ; a language and method which in fact 

 are the result of an elegant development of the original 

 principle of Weiss, and were first independently em- 

 ployed by the famous German mathematician, Grass- 

 mann, Inooint of fact every crystallographer now uses the 

 Millerian formulae, and actually while using the notation 

 of Naumam, prefers to translate it into the simpler 

 symbols of Vliller in order to deduce the determinants 

 rather than employ the earlier modes of calculation. 



Again, whet crystallographer who has had to convert 

 the notation o"" Naumann for the rhombohedral into that 

 j for the hexagoial system, but knows the complexity of the 

 process, and nust recognise the superficial character of 

 that notation ? Moreover, for a distinctive representa- 

 tion of hemi- symmetrical or tetarto- symmetrical forms in 

 language or wfting that carries a scientific meaning, the 

 notation of Navmann is powerless. 



But Prof. Grcth is writing for a German public, and 

 le has to write a book that will be read. It is to be 

 loped that his vork will be widely read, so widely as that 

 lis intelligent countrymen may be prepared, when it 

 eaches a seconoor at furthest a third edition, to accept 

 he change to the Anglo-German notation and methods 

 vhich Weiss, Neimanni Grassmann, Whewell, and Miller 

 five of the greafast names among European crystal- 

 ographers), haveelaborated. 



There remains, however, a word to be said upon the 

 examples selected by Prof. Groth to illustrate this part of 

 his treatise. They are as interesting to the crystal- 

 lographer as they are excellent from the point of view of 

 illustrations ; for the publication of several of them in 

 this form serves to bring together valuable illustrations 

 of the different kinds of merosymmetry, of which some 

 are new, while others have to be sought for only in the 

 memoirs in which they appeared. 



It may have been the result of a practical estimate of 

 the smallness of the number of Englishmen who would 

 have been interested in seeing them, that prevented Herr 

 Fuess, the optical-instrument-maker of Berlin, from 

 sending to the Loan Exhibition a set of the instruments 

 in the improvement of which he has been so largely 

 guided by Prof. Groth. It was, however, a short-sighted 

 view, for the students of this subject are increasing ; the 

 physical laboratories of Oxford and Cambridge, and 

 some London teachers of physics, are, for instance, turn- 

 ing out students quite competent to handle and to appre- 

 ciate such implements of research ; and for all such 

 students the instruments of Soleil and the other French 

 makers represented in the Loan Collection naturally have 

 the greater attraction due to proximity and to their having 

 been for several months where they could be seen and 

 handled by English teachers and their students. 



N. S. M. 



OUR BOOK SHELF 



La Digestion Vegitale, Note sur le Role des Ferments dans 

 la Nutrition des Plantes. Par E. Morren. (Gand, 

 1876.) 



This paper is brought forward by Prof. Morren as a 

 supplement to his observations on carnivorous plants. 

 Its main point is the statement that digestion is not a 

 function exclusively of those plants termed "carni- 

 vorous," but is a process common to all living beings, 

 vegetable as well as animal. Animal digestion is, he states, 

 according to the most approved view, a p'^ocess of fer- 

 mentation consisting essentially in a transformation of 

 colloids into crystalloids, this change being a necessary 

 preliminary to absorption. In the same manner all plants 

 digest ; and the process is precisely analogous to that of 

 animals, and is again essential before assimilation is 

 possible. The ordinary vegetable ferment for the conver- 

 sion of starch into glucose is diastase, which has been 

 detected in barley ; it occurs also in the tubers of the 

 potato, near the " eyes." For the fermentation or diges- 

 tion of nitrogenous substances, albuminoid?, a different 

 ferment is required, and this we have in pepsine, which 

 has been detected lay several observers in the viscid secre- 

 tion of Nepenthes, Drosera, and other insectivorous plants. 

 According to Masters, it occurs also in the nectaries of 

 Hellebortcs ; and a similar substance has long been known 

 in the latex of Carica Papaya. Vegetable digestion is 

 therefore as widely ditfused and as various a phenomenon 

 as animal digestion, and consists in the transformation of 

 the raw insoluble food material into soluble crystalloids 

 capable of assimilation. It takes place chiefly in the 

 " reservoirs of reserve-material " — seeds, underground 

 stems, roots, the bark, the pith. The nutrition of plants 

 is made up of three successive processes : — elaboration, 

 digestion, assimilation. The first consists in the produc- 

 tion, out of its elements, of a carbo-hydrate, and can take 

 place only under the influence of light. Digt^stion con- 

 sists essentially in hydration — as in the conversion of 

 starch into glucose — and is associated with an evolution 



