LECTURE III. 



THE STRUCTURE AND PROPERTIES OF THE PLANT-CELL 

 (continued}. 



I. The Molecular Structure of Organised Bodies. 



WE learned, in the preceding lecture, that cell-wall, 

 protoplasm and nucleus all present indications of structure ; 

 the cell-wall in its stratification and striation, the protoplasm 

 and the nucleus in their fibrillar network. But they possess 

 beyond this a molecular structure which cannot indeed 

 be detected with the microscope, but which can be inferred 

 from their properties. As a conception of this molecular 

 structure is of some importance in assisting us rightly to 

 comprehend many of the phenomena which we shall meet 

 with in the study of living plants, we will enter upon a some- 

 what detailed consideration of it. 



In speaking of the properties of organised bodies the first 

 and most conspicuous was their capacity of absorbing water, 

 their power of " swelling-up " or imbibition as we termed it. 

 When this was first observed it was thought to be peculiar 

 to organised bodies, to bodies, that is, which had been formed 

 by a living organism. It has been subsequently discovered, 

 however, that bodies which had not been formed by a living 

 organism possessed this property, such, for instance, as the 

 acrylcolloid of Wagner and Tollens, and membranes of 

 precipitation of cupric ferrocyanide, of ferric hydrate, etc. 

 In order to include these bodies the meaning of the term 



