REJUVENESCENCE IN NATURE. 175 



investment of the cell; thus in the filaments of the 

 genera CEdogonium and JJlotJiriw. It then often appears 

 surrounded by radiating streaks of mucilage, e. g., in 

 the embryo-sac of the Phanerogaraia,* frequently becomes 

 the starting point and centre of the circulation occurring 

 in such threads of mucilage, as is seen most beautifully 

 in the hairs of the stamens of Tradescantia ;-\ or, finally, 

 it is itself carried along by the current, as is the case in 

 the CharacesR (where, however, it soon vanishes) and 

 Vallisneria.X More rarely the nucleus retains its central 

 position in the hollow cell also, when it appears as if 

 suspended in the centre of the cell by an apparatus of 

 radiating mucilaginous threads, as may be seen most 

 beautifully in 8pirogyra.% In Zygnema it is held in the 

 centre of the cell by a strip of mucilage, which connects 

 two large starch-vesicles, these being again connected 

 with the wall of the cell by radiating mucilaginous 

 filaments, rich in chlorophyll. The FucoideaeH also 

 exhibit a central nucleus, occupying the middle of a 

 delicate circulation-network. In Closterium^ the nucleus, 

 with its colourless mucilaginous envelope, is maintained 

 in the centre of the spindle-shaped cell by the green 

 lamellae of contents, arranged radiantly around the long 

 axis of cell, which lamellae are interrupted by it in the 

 middle of the cell. In many cases it seemed to me to be 

 surrounded, as by a band, by a cavity containing water. 

 In the cells of the delicate links of the antheridium of 

 the Characeae, lastly, the nuclei are so large that they 

 occupy the greater part of the cell, sometimes occupying 

 the centre, sometimes pushed a little to one side. 



* Vide Hofmeister, 1. c, t. ii, f. 18-26. 



t Meyen, 'Pflanzen Physiologie,' ii, t. viii, f. 6-10. 



X Ibid., f. 2, and Sohleiden, ' Gmndziige,' p. 393, f. 91, ' Principles of 

 Sc. Botany,' p. 93, f. 95. 



§ Sohleiden, ' Grundz./ ii, t. i, f. 7 ; ' Principles,' t. i, f. 7. 



II Nageli, ' Zeitschrift,' 1844, p. 43, t. ii, f. 1-3. {Sphacelaria scoparia 

 and Zonaria Pavonia.) Transl. in Kay Soc. public., 1845, p. 222, pi. vii, 

 flg. 1-3. 



% Vide Focke, ' Phys. Studien.,' t. iii, f. 11 and 26; Niigeli, 'Einz. 

 Algen.,' t. vi, c, d, e. 



