352 SCIENCE PROGRESS 



sun-driven activities neither man nor other animals and plants could exist. 

 Green plants are thus the physiologically basal organisms in the evolutionary 

 edifice. Such plants owe their superiority to their capacity to use again not only 

 their own waste products but those of other organisms. In common with other 

 living organisms the green plant produces carbon-dioxide, but in contrast with 

 them it possesses the power of building up again — in the process of carbon 

 assimilation under the influence of sunlight — fresh food material from this sub- 

 stance. A clear conception of the present state of our knowledge of this 

 fundamental process is thus of great importance not only to plant physiologists 

 but to the agriculturist and science workers generally. Messrs. Jorgensen & 

 Stiles have placed such workers under a heavy debt of gratitude by the publication 

 in book form of their review which has recently been appearing in the New 

 Phytologist. Very considerable advances have been made of late years in this 

 field, and it is with the work of the last twenty years that this review deals. It 

 should do much, as the authors hope, to convince those who still doubt the 

 position of plant physiology as an independent science. The great value of the 

 work lies in the fact that it is no mere resume, but is throughout severely critical. 

 We are thus left with a very clear picture of the present position of the subject 

 stripped from the unfounded conclusions and the mists of hypothesis which have 

 obscured some aspects of the process. The authors start with an admirable 

 account of Willstatter's work on the chemistry of the green pigments of the leaf, 

 and they had the happy idea of appending a number of simple laboratory 

 experiments which can be carried out by students. They then deal with the paths 

 of gaseous exchange in the green leaf and with the factors influencing the intake 

 of carbon dioxide ; to the last section the Cambridge school of plant physiology, 

 under F. F. Blackman, have made the largest contributions. Further chapters 

 deal with the products of carbon assimilation, the energy relations in carbon 

 assimilation, and theories of carbon assimilation. As an example of very sound 

 critical treatment we may instance the chapters on the factors influencing the rate 

 of assimilation and on the products of assimilation. The emptiness of the 

 several theories of carbon assimilation is exposed with a ruthless hand, but it will 

 certainly save in future much misguided labour. The review indicates clearly the 

 many directions in which the subject can be profitably pursued. When it is 

 realised that carbon assimilation is the basis of all crop-production, it is clear that 

 on economic as well as on purely scientific grounds a fuller knowledge of this 

 fundamental process must be of the greatest value. With the renewed interest in 

 agriculture in this country it is to be hoped that a serious attack on this problem 

 may not be long delayed. V. H. B. 



ZOOLOGY 



A Critique of the Theory of Evolution. By Prof. T. H. Morgan. 



[Pp. x+ 197, with 95 figures.] (Princeton: University Press; London: 



Oxford University Press, 1916. Price 6s. 6d. net.) 

 THIS is a series of lectures delivered under the Louis Clark Vanuxem Foundation 

 by one of America's best workers and a well-known upholder of Mendelism. 

 The lectures were delivered to a mixed audience, and little if any biological 

 knowledge is assumed. The result is an admirable introduction to the theory of 

 organic evolution. This in itself is very useful, and should be read by all students 

 of biology, as it gives a review of the past work and present position in a concise 

 manner, but nevertheless in a critical spirit. We cannot quite accept all the 

 criticisms, but this is only a matter of detail that detracts but little from the work. 



