266 



NATURE 



[July 23, 1903 



plants which have the capacity of association, and 

 which, to speak metaphorically, are able to use 

 changed conditions as signals for serviceable move- 

 ments. Without selection we cannot conceive the 

 forging of the chain of inherited habit which binds 

 plants to the performance of adaptive movements. 



It is true that we cannot say in what the association 

 consists, and it will doubtless be said that our point 

 of view only differs from that of Klebs in substituting 

 "stimulus" for "conditions." The difference is es- 

 sential, for we take into account natural selection as a 

 universal condition under which all organisms subsist. 



We must be content to differ from Dr. Klebs, who 

 goes so far as to say (p. 162) that the adaptation 

 (Zweckmassigkeit) of organisms is in no way (gar 

 nicht) a scientific problem. We are none the less ready 

 to welcome his researches, of which we proceed to give 

 some account. 



Among the results obtained by Klebs some of the 

 most interesting are the experiments in which, by ap- 

 propriate culture conditions, he converts an inflor- 

 escence into an ordinary vegetative shoot. For in- 

 stance, by making a cutting of the flowering shoot of 

 Veronica chamaedrys and growing the plants in damp 

 air, he converts an organ of limited growth into one 

 of unlimited growth, with leaves differing in size, 

 character of hair and phyllotaxy from those of the in- 

 florescence, and resembling the ordinary vegetative 

 shoot. 



Another interesting series of observations is on 

 Glechoma hederacea, which, if grown in a greenhouse 

 and watered with nutritive solution, never flowers, 

 whereas parts of the same individual plant, grown in 

 small pots in summer and kept cool in winter, flower 

 in the following summer. By special treatment he even 

 compelled flowers to appear on the runners, whereas 

 normally only the upright shoots bear flowers. Ajuga 

 reptans bears runners in the axils of its rosette-leaves ; 

 these form in the autumn new terminal rosettes, the 

 central shoots of which flower in the following spring. 

 This is the normal state of things, but Klebs converted 

 a flowering shoot into a runner by darkness and damp 

 heat, and also produced other curious anomalies of de- 

 velopment. In another experiment on the same type 

 he introduced a runner into the lower end of a cylinder 

 of water, when its normally horizontal growth was 

 changed and it grew straight up until it reached the 

 air, where it once more became horizontal. Klebs de- 

 votes a section of his book to a discussion of the facts 

 of regeneration for which we are largely indebted to 

 Vochting. Klebs points out that we do not even know 

 why the severance of a part from its parent should lead 

 to a regenerative outgrowth of roots and shoots ; he 

 goes on to demonstrate by experiments that in Salix 

 vitellina a branch, without being severed from its 

 parent, can be forced to make roots by submerg- 

 ence in water. He uses this fact as an argu- 

 ment against the adaptive explanation of the 

 behaviour of cuttings. It proves, of course, that 

 some of the phenomena are producible without 

 severance, but the facts of severance remain ; two 

 different stimuli may produce the same result, as in the 

 well-known experiment of Pfetfer in which the root- 

 NO. 1760, VOL. 68] 



hairs of the gemmae of Marchantia develop on the 

 physically lower side and also on the side in contact 

 with a solid body. 



Another section of the book deals with the length of 

 life of plants and the cognate facts on resting periods 

 in vegetable- growth. He shows that Parietaria can be 

 kept in constant flower for two years. That in annuals 

 there is no inherent limit to their development, as he 

 proved by making a series of cuttings of the growing 

 shoots. Again, he compelled the winter buds of Gratiola 

 to germinate (contrary to their habit) without a rest- 

 ing period, by cultivating the plant under water and 

 placing it in a greenhouse in autumn. These may 

 serve as examples of the experimental work in which 

 Dr. Klebs is engaged. It is evidently a research which 

 tests to the full his ingenuity and deterhiination, and 

 it is one in which all naturalists will wish him the 

 success he deserves. 



The book concludes with a section on " Variation and 

 Mutation," which will be useful to old-fashioned 

 evolutionists in showing the trend of certain younger 

 schools of thought. Francis Darwin. 



NITROGEN AND ITS COMPOUNDS. 

 Der Stickstoff und seine wichtigsten Verhindungen. 

 By Dr. Leopold Spiegel. Pp. xii + 912. (Braun- 

 schweig : Vieweg und Sohn, 1903.) Price 20 marks. 

 THE large and ever-increasing amount of work 

 turned out by research chemists in all branches 

 and departments of the science, and the dispersal of 

 the results of investigations throughout a sufficiently 

 extended array of publishing media, awaken the de- 

 mand for some means by which the wealth of newly- 

 acquired knowledge may be made easily accessible ; and 

 the editor or author who undertakes the very tedious 

 but important task of collecting from the different 

 sources and arranging in a summarised form all, or 

 even the most important, facts which have been estab- 

 lished, performs a service to his science for which he 

 does not always receive due credit. j 



The importance of the compounds of nitrogen for | 

 the study of valency and the formation of complex 

 compounds, the important position which they occupy 

 in investigations into the laws of stereochemistry, 

 and, in the case of the carbon compounds, the deter- 

 mining influence of the nitrogen atom on the character 

 of the molecule, have led the author to the compilation 

 of a volume which brings together all the most im- 

 portant known facts with regard to the chemical and 

 physicochemical relationships of this element and its 

 compounds. No separation is made of the organic 

 from the inorganic compounds, but the latter are 

 treated much more fully than the former. With re- 

 gard to the organic compounds of nitrogen, the author 

 has wisely refrained from a duplication of " Beilstein," 

 and has contented himself with pointing out the more 

 important characteristics, and with giving in tabular 

 form the chief representatives of the different groups. 



The whole matter is arranged under the following 

 headings : — the element, halogen compounds of 

 nitrogen, oxygen compounds of nitrogen, sulphur 

 compounds of nitrogen, hydrogen compounds of 



