210 THE MENDEL JOURNAL 



adaptations and responses of plants to a changeful environment. 

 The illustrative examples — which Professor Henslow of course 

 regards as " illustrative proofs " — of direct adaptation are culled 

 from a wide range of plants and plant organs. The structure of 

 stems, spines, and aquatic leaves ; the habits and structure of 

 climbing plants, of succulent plants, of Alpine and Arctic plants ; 

 of epiphytes, parasites, and saprophytes ; the habits and form 

 of swollen roots and tuberous organs ; the phenomena of degener- 

 ation, and the various considerations relating to the origin of 

 monocotyledons, are all called upon to produce their evidence. 

 There are many very excellent illustrations showing the differ- 

 ences produced in plants as responses to varying environments. 

 The type is large and clear and the paper good. 



Having thus recommended the book as a statement of an 

 interesting series of facts, perhaps we may claim the privilege of 

 criticising some of the deductions. We will first consider Professor 

 Henslow' s main deduction. He asks us to believe that species 

 have arisen under " the joint action of the two great factors of 

 evolution — variability and environment — without the aid of 

 natural selection." He contends that plants directly respond to 

 changes in the environment and that in time these changed 

 structures or activities are hereditarily transmitted. He denies 

 in a quite uncompromising manner that evolution depends at all 

 upon the elimination of " unfit " organisms and the maintenance 

 or persistence of the " fit." Granting for the moment, that plants 

 may become permanently modified by responding to the direct 

 action of the environment, and that this change maybe hereditarily 

 transmitted, has Professor Henslow ever inquired how this capa- 

 city to thus respond came into being ? The wide plasticity of 

 plants is an obvious thing. But how did that plasticity arise 

 and how has it been maintained in the vast majority of plants ? 

 Are all plants equally plastic ? Plasticity is as much an inherent 

 quality of a plant as its chlorophyll, its scent, and its form. 

 And is not this plasticity — the capacity of responding to a 

 changing environment — itself the product of evolution by 

 Natural Selection, a matter of the survival of the fittest ? Let 

 us imagine two hypothetical plants, both at the seedling stage, 

 placed in a nearly sterile soil, and in a diffuse light. One of these 

 plants can respond to this harsh environment, and adjusts its 

 metabolism to the conditions. The other cannot, and its kata- 

 bolism goes on at a pace which is consonant with a richer food 

 supply than that available. Clearly the latter must perish, 

 while the former, stunted in growth, survives. The stunted 

 growth is not an effect of the direct action of the impoverished 

 soil, it is merely the manifestation of the inherent capacity of the 

 plant to respond to external conditions. And this particular 



