34 Prof. H. Karsten on the Formation, 



nuclei occur in the position usually occupied by them when the 

 septum is half or completely lignified, although there is no trace 

 of any such structure. In the middle between these two nuclei 

 the third nucleus, belonging to the system of the mother cell, 

 frequently occurs, all three enclosed within the very long and 

 apparently nearly gelatinous membrane of their common mother 

 cell (the original cell-nucleus), which is distinctly recognizable 

 in a nearly round form in the conditions represented in figs. 

 83 & 84. This elongated nuclear cell, with its three nuclei, is 

 also apparently attached by mucoid filaments. 



This occurrence of several nuclei is to be explained by the 

 deficiency of nitrogenous compounds in the water furnishing 

 their nourishment, as appears from the phenomena of the deve- 

 lopment of the septum, to be referred to immediately. 



In the so-called mucoid filaments which are so distinctly 

 recognizable in many Spiroffyra, as for example S. princepg 

 {nitida and jugalis. Kg.), I have observed a movement proceed- 

 ing slowly from the periphery towards the central nucleus, and 

 this in individuals which had been lying for a short time in 

 water containing carbonic acid, and also in the extremities of 

 strongly vegetating plants. 



The mucoid filaments are therefore not solidified cords of 

 plasma, excrescences from the membrane of the secondary cell, a 

 framework for the support of the cell-nucleus floating in the 

 middle of the cell, but a mucilaginous granular fluid, the true 

 cell-juice, the fluid contents of the cell, in and from which the 

 other cellular structures, both the nucleus and the vesicles con- 

 taining secretion-materials, are developed. 



These fluid cell-contents certainly occupy the smallest part of 

 the cavity of the cell, which is almost completely filled by the 

 above-described colourless vesicles (p. 27) (fig. 72), so that they 

 are limited, in the form of a fluid intercellular mat^r, to the 

 spaces left between them by the latter in cells engaged in rapid 

 vegetation. 



Schleiden saw this movement of the cell-juice in the extre- 

 mities of Spirogyra, and supposed that the same took place in 

 the mucoid filaments, in which it was subsequently observed by 

 Nageli ; Kiitzing, on the contrary, threw doubt upon it in both 

 cases. 



The cause of this circulation of the juice of many vegetable 

 cells is very probably to be found in the concurrent lively but 

 chemically difi'erent assimilative energy of the membranes of these 

 tissue-cells and of the secretion-cells (the so-called vacuoles) 

 contained in them. 



That the latter are true cells, and not mere water-filled cavities 

 of the mucilaginous cell-juice, I have already endeavoured to 



