INTRODUCTION ii 



an insight into the chemical architecture of the plant has brought us face to face 

 with questions of the most difficult character, questions which we must leave 

 without being able to give satisfactory answers to them. At the same time, 

 chemical investigation of a selected plant teaches us much that is of importance. 

 In the first place, we find the plant to be composed of elements all of which are 

 found in its surroundings, the soil, water, and air ; and, in the second place, 

 we see that these elements are grouped in the plant into more complex com- 

 pounds than occur in the inorganic environment. We have also seen that the 

 plant takes up its raw materials from this environment, and changes them 

 in its interior. We must now endeavour to make ourselves acquainted more 

 in detail with the absorption of these raw materials. 



Bibliography to Lecture I. 



Berthold, G. 1886. Studien iiber Protoplasmamechanik. Leipzig. 



BRtJCKE, E. 1 86 1. Die Elementarorganismen. Sitzber. Wien. Akad., Mat.-nat. 



Kl. 44, Abt. ii, p. 381 (Ostwald's Klassiker, Nf. 95, Leipzig 1898). 

 BiJTSCHLi. 1882. Unters. uber die mikrosk. Schaume u. d. Protoplasma. Leipzig. 

 BiJTSCHLi. 1898. Unters. uber Strukturen, etc. Leipzig. 

 Ebermayer. 1882. Physiologische Chemie d. Pflanzen, I. Berlin. 

 Fischer, A. 1899. Fixierung, Farbung und Bau des Protoplasmas. Jena. 

 FiJRTH, R. V. 1903. Vgl. chemische Physiologie d. niederen Tiere. Jena. 

 Hammarsten. 1899. Lehrbuch der physiologischen Chemie, 4th ed. Wiesbaden. 

 HoFMEiSTER, F. 1901. Die chemische Organisation der Zelle. Braunschweig. 

 KONIG. 1882. Zusammensetzung der menschhchen Nahrungs- und Genussmittel, 



2nd ed.. Vol. i. Berlin 1882. 

 KoNiG. 1887. Landwirtsch. Versuchsstationen, 48, 81. 

 Reinke and Rodewald. 1881. Unters. aus d. bot. Lab. Gottingen, 2, i. 

 Reinke. 1 88 1. Ibid. 2, 79. 

 Reinke. 1883. Ibid. 3, i. 



Reinke. 1901. Einleitung in die theoretische Biologie. Berlin. 

 Tschirch. 1900. Die Harze und die Harzbehalter. Berlin. 

 Verworn, M. 1894. AUgemeine Physiologie, 3rd ed. Jena 1901. 

 VocHTiNG, H. 1882. Die Bewegungen der Bluten und Fruchte. Bonn. 



LECTURE II 

 THE OSMOTIC CHARACTERS OF THE CELL 



The mode of absorption of nutritive materials may be best studied by 

 a consideration of the process as it occurs in a single cell. If the cell be naked, 

 as it is, for example, in the Myxomycetes, the protoplasm can flow round and 

 absorb solid bodies ; but in the great majority of cases the existence of a rigid 

 cell-wall renders the absorption of solids impossible and compels the plant to 

 be dependent on fluid nutriment, and absorption of water and of substances 

 dissolved in it is almost the only method available in nature by which the 

 plant can obtain its food supply. That water can penetrate both cell-wall 

 and protoplasm is unquestionable, since, as we have already seen, both are 

 capable of swelling in water ; but whether the substances dissolved in the 

 water are also capable of entering is quite another question. As a matter of 

 fact, we shall find that by no means all substances soluble in water are able 

 to enter the cell. When we inquire whether this selective absorption depends 

 on the nature of the cell-wall or of the protoplasm we find ourselves compelled 

 to study the physical laws of diffusion and osmosis, for it is in this category 

 of phenomena that we must include the processes concerned in the absorption 

 of nutritive material by the cell. 



It is well known that when two miscible liquids or solutions, e. g. alcohol 

 and water, or water and an aqueous solution of copper sulphate, are care- 



