Physiologie. 605 



toxicity; and that the excretion from roots and rbizomes of plants 

 is one of the variables of the conditioning factors. 



4. In untreated bog water there are found deposited upon the 

 roots of wheat plants numerous colored bodies as the result of the 

 oxidizing action of roots. The general decay of the root-tips indicates 

 that the oxidizing activity is insufficient to decrease the harmful 

 effects of bog toxins. 



5. It is possible that ecesis, association, and succession of plants 

 depends primarily upon respiration , and that in respiration bog 

 plants differ from other plants. 



6. Treating bog water with an insoluble adsorbing agent is 

 invariably beneficial. 



7. Different physiological phases result from the progressive 

 addition of an adsorbing substance. With coarsergrained materials 

 the low Optimum rate of transpiration is soon succeeded by a mini- 

 mum which is due to the action of toxic substances still present. 



8. Finer-grained insoluble bodies are more beneficial. The res- 

 ponse to toxic bodies when present in small amounts leads to 

 acceleration of growth. The period of growth is more prolonged, 

 and the Optimum and maximum rate of transpiration lie near together. 



9. The adsorptive action of corborundum and humus is about 

 four times greater than that of quartz; the capacity of soils for 

 retaining toxins is therefore higher the greater the content of humus. 



10. The decrease of the poisonous effect of bog water is probably 

 a function of the surface of the particles; it is relatively proportio- 

 nate to the quantity of the solid body used. 



11. In agricultural soils used as adsorbents the presence of the 

 adsorbed unknown toxins replaces normal growth by an abnormal 

 retardation. Fertility is restored through areation, that is, after 

 time enough has elapsed for the oxidation of the injurious bodies. 



12. The contaminated condition of agricultural soils and the 

 consequent decreased physiological activity of the plants grown in 

 them still fürther indicates that xerophily cannot be due to acidity, 

 lack of oxygen, low temperature, etc., of the soil substratum; that 

 is, the factors heretofore cited are only in part the cause of xerophity. 



In view of the evidence presented above, the writer believes 

 that these facts in the action of bog water upon soils justify the 

 conclusion that there are present in bog water and in bog soils 

 injurious substances which are, at least in part, the cause of xero- 

 phily in plants, and of decreased fertility in bog soils. Trelease. 



Dandeno, J. B., Osmotic theories with special reference to 

 van 't Hoff's law. (Bull. Torr. bot. Club. XXXVI. p. 283—298. 1909.) 



A general discussion of osmosis with arguments against van 't 

 Hoff's gas-pressure theory based upon experiments by the author 

 and others. An attraction theory is proposed postulating (1) that a 

 membrane can be less permeable to one liquid than to another and 

 (2) that the molecules of all substances which are soluble in a cer- 

 tain solvent have an attraction for the molecules of the solvent and 

 the molecules of the solvent for the substance in Solution. Trelease. 



Hoffmann, D., Ueber den Einfluss des Kalkmangels auf 



