REVIEWS 495 



No less interesting than the vigorous development of these and other 

 species, such as the blackbird, the starling, gorse, broom, ragwort, etc., is 

 the story of their vicissitudes and the interaction of one species with another. 



Several instances are cited of the diminution of native animals by reason 

 of the increase of introduced species, but with respect to plants the author 

 supports the contention of Cockayne that the native Flora is quite capable of 

 withstanding the invaders except where the natural conditions have been 

 altered by the influence of man . The phenomenon of the frequency maximum 

 followed by a decline in numbers and vigour, so often quoted in respect to 

 the Elodea pest in this country, would appear to have had its counterpart 

 in the history of Cnicus lanceolatus in New Zealand and also of the rabbit 

 within certain areas. The latter, which was formerly a pest in both wet and 

 dry districts, has now disappeared from some of the colder and damper 

 regions . 



The repeated introductions which failed have also their lessons to teach, 

 and indeed the problems upon which these data bear are amongst the funda- 

 mentals of biological distribution. Some of these are considered in the two 

 chapters on the subjects of the interaction of endemic and introduced Faunas, 

 and the alteration of the Flora since European occupation. 



The final chapter on Legislation is an interesting, and at times humorous, 

 commentary on the gradual education of public opinion, whilst the laws 

 themselves are a useful index of the increasing seriousness of the pests 

 concerned. 



As already indicated, the major portion of this work is concerned with 

 the presentation of what is known respecting the history of each species of 

 introduced animal and plant : a catalogue of facts for which biologists owe no 

 small debt to the author, and which the student should place upon his shelf 

 to digest at leisure. E. J. Salisbury. 



Basic Slags and Rock Phosphates. By George Scott Robertson, D.Sc, 

 F.I.C., with a Preface by Edward J. Russell, D.Sc, F.R.S. Cam- 

 bridge Agricultural Monographs. [Pp. xvi + 120, with 8 plates.] 

 (Cambridge : at the University Press, 1922. Price 14s. net.) 



At first sight there would appear no obvious relation between a change in 

 the method of making steel, and the manurial requirements of hay and 

 pasture fields. There is, however, a very real connection ; the slag which 

 separates from the molten metal was shown, forty years ago, to have valuable 

 fertilising properties, and its use— under the name of basic slag — rapidly 

 extended, largely owing to the demonstrations of its beneficial properties 

 at the experimental station at Cockle Park, Northumberland, and elsewhere. 

 Its use has been almost exclusively confined to grass land, although in certain 

 districts, notably in Essex, it is employed instead of superphosphate, on 

 arable land which is deficient in calcium carbonate. The characteristic of 

 basic slag from the agriculturalist's standpoint is its content of phosphate, 

 especially phosphate in an easily soluble form. The older type of slag 

 resulting from a modified Bessemer process was very satisfactory in this 

 respect. Unfortunately for the farmer, the Bessemer process is being 

 rapidly displaced by the basic open hearth method, and the slag produced 

 in this process has usually a lower content of phosphate, which is in a less 

 available form than that produced by the older process. 



There are further difficulties ; slag is a waste product, of little if any 

 interest to the steelmaker, who is not likely to make any alterations involving 

 extra expense in his methods of manufacture for the sake of improving the 

 agricultural value of this waste product ; the supply of slag depends entirely 

 on the demand for steel, and is insufiicient in normal years for the potential 

 demands of agriculture, which have been put by the best authorities at 

 nearly 1,000,000 tons per annum. 



