May 5, 1899.] 



SCIENCE. 



649' 



dealt with. The effects of rough shaking on 

 bacteria and of tensions and torsions on plant 

 tissues are described. Nothing is said in re- 

 gard to the changes that take place in bones, as 

 a result of displacement, etc. The closing of 

 wounded surfaces (in Stentor and Hydra) is 

 said to ' be grossly mechanical.' I may add from 

 observations of my own that, in some cases at 

 least (in Tubularia and in the embryo of Eana), 

 the closing of the wound after injury cannot 

 be explained as grossly mechanical, but is due 

 rather to a movement of the living cells in re- 

 sponse to a stimulus. 



The action of parts of plants in response to 

 contact and the general phenomena of bending 

 in seedlings, etc., can scarcely be included in a 

 definition of growth, even as broadly defined 

 by the author, for while there is an increase 

 in volume on one side there may be a corre- 

 sponding decrease on the opposite side, the vol- 

 ume of the whole plant or part remaining ap- 

 proximately the same. 



A brief account of the effect of gravity is 

 given in Chapter XV. Two classes of effects 

 are distinguished, the first mechanical, "due to 

 gravity, acting on the growing organ as it 

 might on any other heavy body. The second 

 is a vital effect, having no immediate, direct 

 physical relation to the cause. " It seems a little 

 obscure to state that a vital effect has ' no im- 

 mediate, direct physical relation to the cause.' 

 That the connection is a causal connection, 

 even if a remote one, few will be bold enough 

 to deny. The distinction that the author 

 wishes to make is, perhaps, fairly clear, but 

 the words may easily lead to a misconception of 

 what is meant by vital effects. Again, on page 

 417 (in Chapter XVII., dealing with the effect 

 of light upon growth), the author concludes, 

 after showing that the eggs of many (but not 

 all) animals are sheltered from sunlight, ' that, 

 in general, growth does not take place in nature 

 in full sunlight.' It is obvious that in many 

 cases the eggs deposited in the dark are better 

 concealed, and it is not improbable that this 

 may account for their development in the dark. 

 Under these conditions they would become at- 

 tuned to the absence of light. The more rapid 

 growth of plants in the dark is described in de- 

 tail, the effect of colored light on the growth of 



animals and plants, and the direction of growth 

 in reponse to light, are discussed at some length. 



The effect of heat on growth, as well as on 

 the direction of growth (in plants), is dealt with ■ 

 in Chapter XVIII. The interesting fact i» 

 pointed out that under certain conditions the 

 bending of a plant towards the source of heat 

 cannot be explained as the direct result of the 

 heat causing growth on the warmer side, since 

 the concave side is the one turned towards the 

 source of heat. This experiment may well 

 make one question whether or not these phe- 

 nomena of bending are growth phenomena in the 

 ordinary use of the terms. 



In the concluding chapter the cooperation of 

 several factors in normal growth is analyzed. 

 A clear summary of the work of Semper and de 

 Varigny on the growth of water-snails in a cour 

 fined space is given. There is some excellent 

 matter in the few pages of this chapter, al- 

 though here and there one may find fault with 

 the expression rather than with the general 

 sense. The attunement or acclimatization of 

 an organism to its surroundings is emphasized. 

 A tentative hypothesis to account for the at- 

 tunement is offered. This attempt to construct 

 a possible explanation brings clearly to light 

 that the author pictures to himself these ' vital 

 phenomena ' as chemical responses to external 

 agents. The contrast, therefore, so often made 

 in the text between physical and vital effects 

 would seem to be a difference between physical 

 and chemical reactions. If anything more than 

 this is intended it is not included in the final at- 

 tempt at an explanation, although it is stated 

 on a preceding page that the ' specific effects ^ 

 cannot at present be accounted for by known 

 chemical processes, ' but result from peculiari- 

 ties of the specific protoplasms which depend 

 largely upon the past history of each kind of 

 pi'otoplasm.' 



If we have taken issue with the author 

 on a few points it is only because in these 

 the book appears incomplete or imperfect. 

 Taken as a whole it is a valuable addition to 

 our text-books, and the author is to be congrat- 

 ulated on having performed so difficult and 

 arduous a task with success. The careful and 

 exact summaries that are given will be of use 

 to those not having access to the original papers. 



