196 THK PLANT WORLD 



But to return to the book in hand. The subject is treated in three 

 parts: Parti. The facts of variation ; Part II. The causes of variation ; 

 Part III. Variation in its relation to evolution. The three chapters of 

 Part I treat of the measurement of variation, Dimorphism, and discon- 

 tinuous variation and Correlated variation. In treating of Bateson's 

 discontinuous variation De Vries's somewhat similar mutation theory is 

 discussed. The author evidently thinks neither of great importance in 

 the evolution of species. In the seven chapters on the causes of variation 

 much attention is given to Weismann's theory of the germ-plasm and 

 his classification of blastogenic and somatogenic variations is adopted, 

 though some of the difficulties in attempting such a division are evidently 

 recognized. The author finds himself unable to accept Weismann's 

 views entirely. Later on, in discussing the inheritance of acquired or 

 somatogenic characters, a modification of the germ-plasm theory is 

 proposed which accounts for the transmission of variations in various 

 organs on the supposition that these organs produce a secretion which 

 transmits to the determinants of the germ-plasm the necessary stimulus. 

 Even with this important modification we can scarce accept the theory. 



The several so-called laws of variation which have been promulgated 

 from time to time are discussed. To us it seems a misuse of the term 

 "law " to apply it to general statements based upon so few data. The 

 two chapters of Part III treat of the action of natural selection on 

 variations and Adaptive variations. Notwithstanding the great plausi- 

 bility and apparent truth of the theory of natural selection, its experimental 

 demonstration remains yet to be accomplished. The so-called proofs 

 given are scarce of a convincing nature. The question of adaptive 

 variations is also one far from settled. The author, in common with 

 most other writers on the subject, seems to take for granted the entirely 

 passive nature of animate organisms. In view of the known facts of 

 variation it seems to us more probable that protoplasm possesses an 

 inherent tendency or force which may produce variations in organisms, 

 especially when the equilibrium between such organisms and their 

 environment is disturbed. We perhaps rarely appreciate how numerous 

 and delicate are the influences which effect this equilibrium. 



The author's calm and dispassionate treatment of the whole subject 

 is certainly commendable. His own important investigations form no 

 insignificant part of the work. The book is a valuable addition to the 

 literature of evolution and will be read with profit by all interested in 

 the subject. c. l. s. 



