254 SOME ASPECTS OF CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



rhizoids of fern-prothallia and liverworts. In the hairs of aerial 

 plants this rule is reversed, the nucleus lying near the base of the 

 hair; but this apparent exception proves the rule, for both Hunter 

 and Haberlandt show that in this case growth of the hair is not 

 apical, but proceeds from the base ! Very interesting is Haberlandt's 

 observation that in the regeneration of fragments of Vanchcria the 

 growing region, where a new membrane is formed, contains no 

 chlorophyll, but numerous nuclei. The general result, based on the 

 study of a large number of cases, is in Haberlandt's words that 

 "the nucleus is in most cases placed in the neighbourhood, more or 

 less immediate, of the points at which growth is most active and 

 continues longest." This fact points to the conclusion that " its 

 function is especially connected with the developmental processes 

 of the cell," 1 and that " in the growth of the cell, more especially 

 in the growth of the cell-wall, the nucleus plays a definite part." 

 Korschelt's work deals especially with the correlation between 

 form and position of the nucleus and the nutrition of the cell; 

 and since it bears more directly on chemical than on morphologi- 

 cal synthesis, may be only briefly reviewed at this point. His 

 general conclusion is that there is a definite correlation, on the 

 one hand between the position of the nucleus and the source of 

 food-supply, on the other hand between the size of the nucleus 

 and the extent of its surface and the elaboration of material by 

 the cell. In support of the latter conclusion many cases are brought 

 forward of secreting cells in which the nucleus is of enormous size 

 and has a complex branching form. Such nuclei occur, for example, 

 in the silk-glands of various lepidopterous larvae (Meckel, Zaddach, 

 etc.), which are characterized by an intense secretory activity con- 

 centrated into a very short period. Here the nucleus forms a 

 labyrinthine network (Fig. n, /?), by which its surface is brought to 

 a maximum, pointing to an active exchange of material between 

 nucleus and cytoplasm. The same type of nucleus occurs in the 

 Malpighian" tubules of insects (Leydig, R. Hertwig), in the spinning- 

 glands of amphipods (Mayer), and especially in the nutritive cells 

 of the insect ovary already referred to at p. 114. Here the develop- 

 ing ovum is accompanied and surrounded by cells, which there is 

 good reason to believe are concerned with the elaboration of food 

 for the egg-cell. In the earwig Forficula each egg is accompanied 

 by a single large nutritive cell (Fig. 115), which has a very large 

 nucleus rich in chromatin (Korschelt). This cell increases in size 

 as the ovum grows, and its nucleus assumes the complex branching 

 form shown in the figure. In the butterfly Vanessa there is a group 



1 i.e., p. 99. 



