2i6 SECTIONAL ADDRESSES 



is exceptionally complete. Indeed, it looks very much as if some 

 altogether new technique is required for any advance to be made in this 

 direction, and in this connection I may refer to some remarks made by 

 Sir William Bragg last November in his Anniversary Address to the Royal 

 Society. He pointed out that there is to-day a very considerable interest 

 in magnitudes which are too small to be examined under the microscope 

 and too large to be studied conveniently by X-ray methods. While with 

 the microscope it is possible to observe the presence of particles with a 

 diameter of about o-i5(ji. (1,500 A.U.) and while the ultramicroscope can 

 reveal the presence of particles as small as 5m[ji (50 A.U.), neither the 

 microscope nor the ultramicroscope can reveal any details of structure 

 in objects as small as this. On the other hand. X-ray methods have 

 enabled the arrangement of atoms and molecules to be determined with 

 great accuracy, but they do not enable the details of larger structures 

 to be determined. The invention of a method for determining the 

 structural details of particles larger than those with which X-ray analysis 

 can deal, and which are yet too small for the microscope to resolve, could 

 not fail to provide the general physiologist with a powerful weapon with 

 which to attack the problem of protoplasmic constitution. 



At present, then, we must be content with recognising in the protoplasm 

 a system in which an essential feature is the possession of a large internal 

 surface, with all that this involves, in which there are various phases of 

 different chemical composition, a composition roughly but by no means 

 accurately known. One of the characteristics of this system is that, in 

 so far as it can be regarded as a system in equilibrium, it is in a state of 

 dynamic, not static, equilibrium, for all the time it is absorbing oxygen 

 and giving out carbon dioxide. The process does not end in this, for it 

 involves the loss of material, if not from the protoplasm itself, from 

 material held in the protoplasmic complex, and this material must there- 

 fore sooner or later be replaced, so that the respiration process must in 

 any case be linked up with a movement of material into the cell , from the 

 outside environment, either directly from this or through the medium of 

 some other cell or cells of the plant body, most frequently indeed also 

 after profound chemical changes in the material so absorbed. 



That plants, like animals, absorb oxygen and give out carbon dioxide 

 was recognised by Ingen-Housz and de Saussure towards the end of the 

 eighteenth century, but for long the greatest confusion of ideas prevailed 

 on this question, a confusion which was only dispersed by Sachs with 

 the publication in 1865 of his book on the Experimental Physiology of 

 Plants. Sachs not only made clear the parts played by the respective 

 gaseous exchanges involved in photosynthesis and respiration, but he 

 laid stress on the universality of the respiration process, and emphasised 

 the fact that it is a property of every living cell. Thus, in his text-book 

 of Botany published in 1868 he wrote : ' The respiration of plants con- 

 sists, as in animals, in the continual absorption of atmospheric oxygen 

 into the tissues, where it causes oxidation of the assimilated substances 

 and other chemical changes resulting from this.' And further : ' But 

 in all the other organs also — in every individual cell— respiration is con- 

 stantly going on ; and it is not merely the chemical changes connected 

 with growth that are dependent on the presence of free oxygen in the 



