514 GENERAL PHYSIOLOGY 



tinued to show its normal vital phenomena. While, therefore, the 

 experiments of Klebs prove that the nucleus is necessary for the 

 formation of cellulose, those of Demoor show that the protoplasm 

 also takes part in its production. In other words, cellulose can be 

 formed only by the combined action of nucleus and protoplasm. 



Besides these experimental results, a considerable number 

 of morphological observations upon very different kinds of cells 

 exist, all pointing toward an active exchange of substance between 

 nucleus and protoplasm. Of great interest are the positions of 

 the nucleus relative to certain substances that are produced or 

 taken in by the cell, which have been demonstrated by Haber- 

 landt upon plant-cells and by Korschelt upon animal- cells. 

 Haberlandt's investigations ( '87, '89) have reference to the pheno- 

 mena of growth of the cell-membrane. In a wide range of ma- 

 terial he has established the fact that in certain cases the nucleus 

 exists at the place at which growth-processes are localized. Such 

 cases are the following: where local growth of the cell-wall is 

 necessary to its final form, such as in the thickening on the 



FIG. 253. A, An epidermis-cell of a foliage leaf of Luzula maxima. The nucleus lies in the middle 

 of the cell. B, Epidermis-cells of a leaf of Cypripedium insigne. The upper cell-wall is 

 thickening ; the nuclei lie upon it. C, Epidermis-cell of a leaf of Aloe vermcosa. A swell- 

 ing is being formed upon the upper cell-wall; upon it lies the nucleus. (After Haberlandt.) 



outer side of epidermal cells, in the formation of ridges upon 

 the guard-cells of stomata, and in the rudiments of root-hairs 

 that develop by apical growth at the growing point of roots ; and 

 where regeneration of an artificially injured cell-wall takes place; 

 in brief, wherever a special development of material for the cell- 

 wall takes place (Figs. 253 and 254). But before the beginning 

 and after the cessation of these various phenomena of growth the 

 nucleus takes no definite position in the cell (Fig. 253, A), 



These comprehensive observations of Haberlandt are paralleled 

 by the striking zoological researches of Korschelt ('89). Korschelt 

 has studied chiefly the ova and secreting-cells of insects. In the 

 egg- tubes of the ovaries of Dytiscus marginalis, a large water-beetle, 

 the ova are arranged in succession like a string of pearls and 

 separated from one another by a so-called nutrient chamber. This 

 chamber consists of cells which produce and give off nutrient 

 material to the ova. The behaviour and the position of the nuclei 

 of the ova toward this nutrient material is very characteristic (Fig. 

 255). From the chamber the nutrient material extends into the 



