366 SCIENCE PROGRESS 



chemical facts. The complex problems that the chemistry of chlorophyll presents 

 are stated and to a remarkable extent solved, and yet hypotheses as to the function 

 of the pigment in the plant are neither advanced nor discussed, with the exception 

 of a few very suggestive paragraphs in the first chapter (see pp. 24 and 25). 



After the first chapter, in which the bearing of this new work upon the con- 

 stitution of chlorophyll is considered, chapters are devoted to the methods of 

 extraction and separation of the various pigments of the plant chloroplast. 

 It is not too much to say that these chapters, which contain a considerable 

 account of previously unpublished methods, will go far to revolutionise the crude 

 methods of extraction at present in use in botanical laboratories. 



It is very interesting to learn that with their new methods Willstatter and Stoll 

 are able to obtain preparations of pure chlorophyll from some kilogrammes of 

 dried leaves within so short a space of time as one day and with a yield of some 

 6\ grammes of chlorophyll per kilogramme of dried leaf powder, a yield which 

 probably represents 75 per cent, of the available pigment. 



The genesis of the new methods seems to lie in the fact that the dried leaf 

 material does not readily yield its pigment to pure organic solvents, but that 

 extraction is rapid in, for instance, acetone containing some 1 5 per cent, water, 

 The water seems to alter the colloidal nature of the matrix in which the chlorophyll 

 is retained and it is then readily obtained in solution. Attention may be specially 

 drawn to an interesting feature of the book contained in Chapter II. This consists 

 of descriptions of a series of experiments upon a conveniently reduced scale, by 

 means of which the reader may acquaint himself with the general principles of 

 the quantitative methods to be described in detail in subsequent chapters The 

 majority of these experiments should subsequently find their way into laboratory 

 courses in plant physiology. 



The isolation of the two chlorophylls a and b is fully described, and full details 

 given of the long and difficult processes by which quantitative separation is effected ; 

 the ratios of these two components in different chlorophyll extracts is compared, 

 and the fact brought out that they occur in surprisingly constant proportions 

 in different plants. The separation and isolation of the two yellow pigments 

 xanthophyll and carotin is also described and their quantitative distribution 

 compared. The constant occurrence and relatively constant distribution of 

 these two pairs of pigments is of great physiological interest, particularly as the 

 two chlorophylls, like the two yellow pigments, differ in their oxygen content. 



But there are innumerable facts of interest in this book ; it must suffice here to 

 state briefly certain other problems to which space is prominently devoted. 



The relation of the crystallin chlorophyll to the amorphous pigment and its 

 formation through the agency of the enzyme chlorophyllase are fully described. 



The pigments of the Brown Algae are fully discussed, the view confirmed that 

 phycophaain has no existence in fresh material, the fact established that chloro- 

 phyll a is practically the only one of the two normal chlorophylls present, and 

 three nitrogen free pigments fully described, carotin, xanthophyll, and fuco- 

 xanthin. 



Then follows a long series of chapters dealing with the extensive researches 

 that have been carried out upon the various derivatives of chlorophyll, the long 

 series of magnesium containing derivatives, the magnesium free derivatives which 

 give rise to the various porphyrins, bodies allied to the hasmatin derivatives, the 

 alcohol phytol which enters into the composition of amorphous chlorophyll, etc. 

 It is impossible in a brief review to deal adequately with the great amount of 

 valuable matter that is contained in the book, but sufficient has probably been 



