346 CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



part not only in the operations of synthetic metabolism or chemical 

 synthesis, but also in the morphological determination of these opera- 

 tions, i.e. the morphological synthesis of Bernard a point of capital 

 importance for the theory of inheritance, as will appear beyond. 



Convincing experiments of the same character and leading to the 

 same result have been made on the cells of plants. Francis Darwin 

 ('77) observed more than twenty years ago that movements actively 

 continued in protoplasmic filaments, extruded from the leaf-hairs of 

 Dipsacus, that were completely severed from the body of the cell. 

 Conversely, Klebs ('79) soon afterward showed that naked proto- 

 plasmic fragments of Vancheria and other algae were incapable of 

 forming a new cellulose membrane if devoid of a nucleus; and he 

 afterward showed ('87) that the same is true of Zygnema and CEdo- 

 gonium. By plasmolysis the cells of these forms may be broken up 

 into fragments, both nucleated and non-nucleated. The former sur- 

 round themselves with a new wall, grow, and develop into complete 

 plants ; the latter, while able to form starch by means of the chloro- 

 phyll they contain, are incapable of utilizing it, and are devoid of the 

 power of forming a new membrane, and of growth and regeneration. 

 A beautiful confirmation of this is given by Townsend ('97), who finds 

 in the case of root-hairs and pollen-tubes, that when the protoplasm is 

 thus broken up, a membrane may be formed by both nucleated and 

 non-nucleated fragments, by the latter however only when they remain 

 connected with the nucleated masses by protoplasmic strands, however 

 fine. If these strands be broken, the membrane-forming power is 

 lost. Of very great interest is the further observation (made on leaf- 

 hairs in Cucurbitd) that the influence of the nucleus may thus extend 

 from cell to cell, an enucleated fragment of one cell having the power 

 to form a membrane if connected by intercellular bridges with a 

 nucleated fragment of an adjoining cell (Fig. 161). 



2. Position and Movements of the Nucleus 



Many observers have approached the same problem from a dif- 

 ferent direction by considering the position, movements, and changes 

 of form in the nucleus with regard to the formative activities in the 

 cytoplasm. To review these researches in full would be impossible, 

 and we must be content to consider only the well-known researches 

 of Haberlandt ('77) and Korschelt ('89), both of whom have given 

 extensive reviews of the entire subject in this regard. Haberlandt's 

 studies related to the position of the nucleus in plant-cells with 

 especial regard to the growth of the cellulose membrane. He deter- 

 mined the very significant fact that local growth of the cell-wall is 

 always preceded by a movement of the nucleus to the point of growth. 

 Thus, in the formation of epidermal cells, the nucleus lies at first near 



