Mabch 4, 1898.] 



SCIENCE. 



319 



The mechanics of absorption, excretion and 

 secretion, diosmotic and osmotic properties of 

 the cell with regard to fluids and gases have 

 received such numerous and important addi- 

 tions that it would be possible to point them 

 out only by recounting the summaries of the 

 sections, which space does not permit, but much 

 of the author's own work is briefly summarized 

 here for the first time. 



This is the first general text issued since the 

 researches of Boehm, Askenasy, Strasburger, 

 Schwendener, Dixon and Joly upon the ascent 

 of sap were published, and the Jaminiau chain, 

 the intermittent activity of living cells, the lift- 

 ing power of transpiration and the tensile 

 strength of water are alike shown to be incom- 

 petent to account for the facts. Professor 

 Pfefier believes that whatever the impelling 

 force may be, and the participation of living 

 cells is not barred, the path of the current lies 

 through the tracheal lumina and pits. 



Transpiration is recognized as a necessary 

 means for the distribution of the mineral ele- 

 ments in the plant, as a facilitation of gas diffu- 

 sion, as a regulator of temperature, and the 

 surmise is hazarded that it also may exercise a 

 general tonic effect necessary for the maturity 

 and welfare of the plant. A clear presentation 

 of the relation of stomatal, cuticular and len- 

 ticular transpiration is made, as well as of the 

 factors influencing these processes and the prin- 

 cipal adaptations. 



Bleeding and the phenomena of root-pressure 

 are held to be due to the active secretory agency 

 of living cells, in the root and stem, though 

 plasmolytic agencies, as in nectaries may some- 

 times play a part in the process ; and no essen- 

 tial difference from ' guttation' is exhibited. 

 The water-pores and hyathodes of plants in 

 moist localities may provide an outlet for 

 water to maintain the upward stream, impos- 

 sible by transpiration. 



The chapter on nutrition contains 168 pages, 

 in which all of the more important literature of 

 the subject finds place, and it is impossible in 

 the limits of this review to cite even a majority 

 of the new and modified points of view given. 

 In the consideration of the general metabolic 

 activity of the organism all material is divided 

 into three groups, viz. : constructive substances 



in the permanent structure of the organism, 

 plastic substances capable of participation in 

 the metabolic processes, and aplastic substances 

 incapable of being used further in the nutri- 

 tion of the organism. The last group naturally 

 overlaps the first named. 



Assimilation is used in the broadest sense to 

 denote all physiological processes, or progres- 

 sive chemical metamorphoses by which plastic 

 or trophic substances are built up. According to 

 the source of energy specific processes are de- 

 signated as ' Photosynthese,' ' Chemosynthese,' 

 'Electrosynthese,' etc. 



By photosynthesis is meant the formation of 

 plastic material from carbon compounds, COj, 

 (possibly COCLa, COS, CO (NH,),,) and water 

 by the agency of the chlorophyll apparatus and 

 sunlight, a sense in which it has been used by the 

 reviewer since 1894, though not in agreement 

 with the proceedings of the Madison Botanical 

 Congress. (See editorial review. Botanical Ga- 

 zette, Vol. 19, p. Sil. 1894.) 



Professor Pfeffer points out that the relation 

 of ehorophyll to the ground substance of the 

 chloroplast is unknown, that the optical extinc- 

 tion of portions of the spectrum may or may 

 not be coincident with photosynthetic activity, 

 and that the intermediate steps in the formation 

 of carbohydrates in this manner are unknown. 

 The recent results of investigation upon the in- 

 dependent action of chloroplasts are detailed. 



The nitrobacteria are instanced as the only 

 organisms having the power of formation of 

 carbohydrates from CO, by synthetic methods 

 and by means of chemical energy. 



The author distinguishes between saprophytic 

 and symbiotic nutrition, using the former term 

 only in connection with plants which take up 

 organic food unaided. According to this clas- 

 sification the only seed-forming plants truly and 

 entirely saprophytic are confined to a single 

 genus. With regard to the general relation to 

 organic food, plants are allotropio, mixotropic 

 or autotropic. The results bearing upon the 

 acquisition of nitrogen are brought together 

 in orderly array, but our information on this 

 phase of nutrition is at best very incomplete. 



The discussion of the metabolic changes in 

 the organism is enriched by the addition of an 

 enormous mass of detail, yet it is to be said that 



