PHYSIOLOGICAL RELATIONS OF XLX^LEUS AND CYTOPLAS. 



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the centre, but as the outer wall thickens, the nucleus moves toward 

 it, and remains closely applied to it throughout its growth, after which 

 the nucleus often moves into another part of the cell (Fio-. 162, A B) 

 That this is not due simply to a movement of the nucleus toward the 

 air and light is beautifully shown in the coats of certain seeds, where 

 the nucleus moves, not to the outer, but to the inner wall of the cell, 

 and here the thickening takes place (Fig. 162, C ). The same positi 



on 



Fig. 162. — Position of the nuclei in growing plant-cells. [Haberlandt.] 



A. Young epidermal cell ol Liizula with central nucleus, before thickening of the membrane. 

 B. Three epidermal cells of Monstera, during the thickening of the outer wall. C. Cell from the 

 seed-coat of Scopulina, during the thickening of the inner wall. D. E. Position of the nuclei dur- 

 ing the formation of branches in the root-hairs of the pea. 



of the nucleus is shown in the thickening of the walls of the guard- 

 cells of stomata, in the formation of the peristome of mosses, and in 

 many other cases. In the formation of root-hairs in the pea, the pri- 

 mary outgrowth always takes place from the immediate neighbourhood 

 of the nucleus, which is carried outward and remains near the tip of 

 the growing hair (Fig. 162, D, E). The same is true of the rhizoids 

 of fern-prothallia and liverworts. In the hairs of aerial plants this 



