BOOK REVIEWS. 



253 



" The Heredity of Acquired Characters in Plants." By Rev. Professor 

 G. Henslow, M.A., V.M.H. 8vo., 107 pp. (Murray, London, 1908.) 

 6s. net. 



This little book contains the grounds upon which the learned author 

 bases the belief he so strongly holds, that acquired characters in plants are 

 hereditary, and that all hereditary characters have at some time or other 

 been "acquired." He defines "acquired characters " as "any change of 

 structure (morphological or anatomical) from the normal characters of 

 any part or parts of a plant (i.e. in comparison with others of the same 

 species or genus which have not changed at all) through the means 

 of a response to some new and direct action of the external influences 

 of the environment or ' changed conditions of life.' " 



No one who gives any thought to the question can fail to be struck 

 with the adaptive structures exhibited by plants and by the fact that the 

 progeny of one plant may vary greatly according to the conditions under 

 which it is found. The assumption that plants can vary so as to acquire 

 any adaptive character and that such acquired characters are hereditary 

 affords an easy and obvious explanation of many of the phenomena we 

 may observe on a country walk. Indeed, the explanation appears a 

 little too obvious, and in reality the question is beset with difficulties, 

 as are most questions connected with the phenomena exhibited by living 

 things. 



Variations appear to be of two species. There may be variations 

 in kind, so that a plant possesses a character or it does not ; for instance, 

 a pea may possess the character that makes for tallness, or that character 

 may be absent, and the pea will then be dwarf, and with the dwarfness 

 other characters entirely dependent upon it will be exhibited. On the 

 other hand, variations may be in degree. A tall pea may be more or less 

 tall, a dwarf more or less dwarf ; but recent experiments seem to show 

 there to be a mark of delimitation between the two. In this book, 

 although here and there some hint of the existence of two species of 

 variation is given, yet nowhere is it plainly stated that these two species 

 exist. 



Very frequently one finds that plants grow where they can, not where 

 they can grow best. There are many instances known of plants which 

 hold their own in a certain place, but which when removed to another 

 situation grow with such vigour as to become the dominant feature of the 

 vegetation. We may interpret this in two or three ways, but it would 

 appear quite probable that the plant' was better adapted to an environ- 

 ment different from its original one. That is to say, its adaptation to its 

 environment was imperfect. It is not obvious why, if it were able to 

 adapt itself so far, it could not adapt itself perfectly. As Darwin pointed 

 out, there are many adaptations to environment which fall short of 

 perfection. Why should self -adaptations to environment be imperfect? 



Again, there frequently appears to be no direct correlation between 

 the habitats (environment) of two distinct varieties of a species and 

 their characters. Not far from where we are writing one may find 

 the common form of the ling (Calluna vulgaris) growing with its 

 branches intertwined with the hoary variety incana. Are these both 

 equally adapted to their environment, and if so, why did they not vary 



