i64 



NATURE 



[December 8, 1910 



have their limitations, and when he passes from fresh 

 to salt water (metaphorically speaking) he appears 

 somewhat "out of his element." Otherwise he would 

 not have quoted antiquated and rejected notions re- 

 garding the growth of salmon after its migration to 

 the sea in the face of the well-ascertained results of a 

 vast amount of more recent research. Again, the 

 author's account of the life-history of the eel is not 

 abreast of current knowledge, since he makes no men- 

 tion of the most iinportant and not so very recent 

 discovery of the breeding-grounds of this species all 

 along the eastern shelf of the Atlantic basin. Read- 

 ing M. Gudnaux's account, one would suppose that 

 the latest word on the subject of the eel had been said 

 by Signors Grassi and Calandruccio, which is not so. 

 Then, again, the fear (casually expressed, it is true) 

 lest certain species of pelagic sea fishes, such as the 

 pilchards (sardines) off the west coast of France, be 

 in danger of extermination through over-fishing is 

 probably unwarranted, and argues a lack of know- 

 ledge of the conditions of life in the sea. Finally, 

 returning to the salmon, it will surely surprise anyone 

 who has some knowledge of the Highlands of Scot- 

 land and of the rigorous restrictions to which salmon- 

 fishing is subjected in this region at the present day, 

 to be told that :— 



" Aujourd'hui, c'est dans ce pays [viz., Scotland] 

 que les domestiques sont obliges de stipules k I'avance 

 que le saumon no paraitra trop fr^quemment dans leur 

 ordinaire ! " 



These happy days are almost ancient history. But 

 such matters are, after all, quite on the fringe of 

 M. Gu^naux's subject. Enough has been said to 

 indicate that the book is a small mine of information, 

 and should be consulted by all whose business or 

 pleasure brings them face to face with any of the 

 difficult problems connected with fresh-water pisci- 

 culture. William Wallace. 



.4 CYCLOPEDIA OF AGRICULTURAL 

 CHEMISTRY. 

 Kleines Handworterbuch der Agrikulturchemie. By 

 Dr. Max Passon. Two vols. Erster Teil, Aadl- 

 kynurensaure. Pp. iv + 454. Zweiter Teil, Lab- 

 zymogen. Pp. 415. (Leipzig : Verlag von Wilhelm 

 Engelmann, 1910.) Price 22 marks. 

 'T^HESE two volumes bear striking testimony to the 

 -L enormous strides made during the last twenty 

 years in agricultural chemistry. Only within very 

 recent times has the need for a cyclopaedia been felt; 

 previously the chemist could always pull through if 

 he possessed one of the larger analytical treatises and 

 had access to a set of the Jahresberichte for agricul- 

 tural chemistry. Rapid progress set in when the sub- 

 ject was emancipated from the analytical stage ; when 

 the chemist, instead of being confronted with an inter- 

 minable succession of analyses of manures, feeding- 

 stuffs, and soils, was free to study the numerous 

 problems presented by the plant in its relation to the 

 soil, on the one hand, and the animal on the other. 

 To the popular mind the agricultural chemist is 

 still an analyst, and beyond doubt the analyst is more 

 necessary than ever he was; but the distinction be- 

 NO. 2145, VOL. 85] 



tween the two is fast becoming as sharp as in pure 

 chemistry. This process of segregation is going even 

 further, and already men are specialising in the 

 various branches of agricultural chemistry itself. 

 Hence the need of reference books like the present 

 volumes. 



One of the features of the book is the treatment of 

 laboratory operations. The ordinary methods are 

 dealt with in some detail, there are numerous illus- 

 trations, and, where necessary, tables of figures. Even 

 such minor but important processes as the recovery of 

 platinum, silver, &c., from their residues find a place. 

 In addition, a number of tests are given, and methods 

 for finding whether nitrogen is present as an amide 

 group, an amino-acid, or an ammonium salt. 

 Although these are probably the fullest articles in the 

 volumes they are rather restricted in their scope, atten- 

 tion is devoted almost exclusively to German methods, 

 little space being given to those in use elsewhere. In 

 several instances the book suffers in consequence. 

 Thus we find the methods for the mechanical analysis 

 of soils are very incomplete ; the separations are car- 

 ried only far enough to include material more than 

 02 mm. in diameter, all below this limit being 

 grouped together as fine sand, &c. This is very un- 

 fortunate, because it is now known that the finer 

 fractions — those falling between o"2 and 0*04 mm., 

 between 004 and o'oi mm., between 001 and o'oo2 

 mm., and below 0002 mm. — really play a controlling 

 part in soil fertility; indeed, no soil analysis can be 

 fully interpreted without knowing them. 



The book is, however, more than a laboratory 

 manual, and space is found for some of the great 

 generalisations and theories that have played a part 

 in the development of the subject. The treatment is 

 all too brief, especially when one remembers the im- 

 portance rightly attached in Germany to theoretical 

 considerations. Liebig's famous "law of the mini- 

 mum " is stated, but its modern developments are not 

 mentioned. "The growth of the plant is governed by 

 the quantity in the soil of that food constituent which 

 is present in the smallest amount." This generalisa- 

 tion has proved of great value in agriculture, but it 

 is now merged in the wider conception of limiting 

 factors, which we should like to have seen discussed 

 in the book. It is now recognised that certain re- 

 quirements must be fulfilled before plants will grow 

 well — there must be ample water, air, warmth, food, 

 light, and no injurious substance must be present. 

 Any increase in one of these factors may lead to an 

 increased crop production, but the increase is soon 

 limited by the insufficiency of some one or more of the 

 other necessary factors. If all are increased, the limit 

 is finally set by the plant itself. In general, however, 

 modern hypotheses are not given ; we have been un- 

 able to find any mention of the well-known toxin- 

 excretion theory of Whitney, which supposes that 

 infertility arises through the excretion of toxic sub- 

 stances by plant roots. Whether it ultimately turns 

 out correct or not, this theory has led to so much 

 investigation that it deserved a place. 



A critic could easily point out much more that has 

 been omitted. But he would find it difficult to see 

 how it could be otherwise within the limits of two 



