40 STRUCTURAL BOTANY 



and midway between the two daughter-nuclei. It is 

 formed by the protoplasm itself. Generally the new 

 cell-wall does not stretch all the way across the cell, 

 but has to be completed at the sides later on (see 

 Tig. 17). The nucleoli disappear during the division, 

 and their substance appears to pass out into the pro- 

 toplasm. New nucleoli make their appearance in each 

 of the daughter-nuclei, which soon assume the size 

 and structure of the nucleus before division. We see, 

 then, that the essential points in vegetative cell-forma- 

 tion are the division of the nucleus into two exactly 

 similar halves, and the formation of a cell-wall between 

 them, separating the protoplasm of the cell into two 

 distinct parts. 



d. Continuity of the Protoplasm 



We have hitherto been considering the structure of 

 the individual cells of which a plant is built up ; the 

 research of the last twenty years, however, has shown 

 that in all vegetable tissues, the protoplasm of each 

 cell is in communication with that of its neighbours 

 by means of excessively fine protoplasmic fibrils, which 

 extend through the cell-wall from one cell to another. 

 The perforations through which the connecting proto- 

 plasmic fibrils pass are extremely minute, but are often 

 very numerous (see Fig. 18). The importance of the 

 discovery lies in the fact that we now know that the 

 living matter in the plant is continuous, and not 

 absolutely severed into isolated portions by dead cell- 

 wall. The plant, in fact, is, as a whole, a living proto- 

 plasmic body, supported, but not interrupted, by the 

 skeleton of cell- walls. 



