20 THE JOURNAL OP BOTANY 



estimated by others. At first glance, nothing could appear simpler 

 or more obvious than the proposition that, since the reactions by 

 which any given substance is recognized macrochemically will be 

 yielded by that substance when the test is made under the micro- 

 scope, the different kinds of cell-walls and cell-contents may be 

 demonstrated by the use of reagents which either impart charac- 

 teristic colours to walls and contents, or act as selective solvents, 

 dissolving some of the walls and contents and leaving others un- 

 dissolved, or produce precipitates whose nature furnishes evidence 

 regarding the character of the substance that has united with the 

 reagent to produce the precipitate. As is well knowm, valuable 

 results have been obtained in chemistry and geology by the 

 application of the microscope to the examination of small quan- 

 tities of solid and liquid substances, but when we are dealing with 

 the cells and tissues of plants, considerable difficulties are pre- 

 sented. The microchemical examination of a drop of water, even 

 when several substances are dissolved therein, is a simple matter 

 as compared with that of a plant cell containing perhaps a hundred 

 different chemical compounds, and among these various colloidal 

 bodies which interfere with crystallization and other reactions. 



On the other hand, it must be remembered that in many cases 

 a microchemical test may afford the only practicable method for 

 the detection of substances which are present in quantities too small 

 for macrochemical analyses, and that microchemical methods, 

 used with due precautions, have many striking additional ad- 

 vantages. 



The pros and cons of the subject are, however, admirably 

 discussed by Molisch in the introduction to the book under 

 review, which will be found of the utmost service to students of 

 every branch of pure and applied botanical science. The author 

 states that he has been engaged in the preparation of this book 

 for more than twenty years, and that practically every reaction 

 described has been repeatedly tested by him, the result being that 

 the work stands in a class quite apart from the numerous com- 

 pilations devoted partly or entirely to vegetable microchemistry 

 which have hitherto been published. Throughout his descrip- 

 tions of the modes of occurrence and methods of detection of the 

 various substances present in the cell-walls and wall-contents, the 

 author emphasises the need for caution in the interpretation of 

 results and for obtaining confirmatory reactions in those cases 

 where at present we have no reliable and certain method of 

 demonstrating the presence of a given substance — e.g., various 

 glucosides and alkaloids — in the cell, or where the reaction is 

 with probability or certainty to be ascribed to post-mortem 

 chemical change, and so on. The author might with reason and 

 advantage have pointed out still more explicitly that, while many 

 of the results obtained by macrochemical analysis of plant extracts 

 are vitiated by the neglect of investigators to distinguish between 

 substances actually present in plants and those formed in the 

 processes of extraction and testing, the necessity for caution in 

 the interpretation of results is infinitely greater in the case of 



