SO PKOTOPLASMIC THEORY BEFORE 1860 MOHL. 



these are originally isolated, and very frequently present 

 a most deceptive resemblance to delicate-walled cells ; 

 subsequently, however, they become blended together in 

 many directions ; the protoplasm is then accumulated at 

 one side in the vicinity of the nucleus ; on the other side it 

 coats the inside of the primordial utricle, and these two col- 

 lections are connected together by thread-like processes, 

 which are sometimes simple and sometimes branched, so 

 that the nucleus appears as if suspended in a spider's web in 

 the centre of the cell. An internal movement of the protoplasm 

 now begins to be visible originally no definite arrangement 

 can be perceived in it ; but the more the protoplasm changes 

 from the uniform mass which it originally formed into the con- 

 dition of threads, the more distinctly it can be seen that each 

 of these threads represents a thinner or thicker stream, which 

 in one thread flows from the nucleus to the periphery, turns 

 round there and flows back again in another thread. The 

 thickness, the position, and the number of these threads are 

 subject to constant change, which shows beyond a doubt that 

 the currents move freely through the watery cell sap and are 



not enclosed in membranous canals The nucleus retains 



its central position in many cases even when the cell is fully 

 developed ; e.g,, in Zygnema, but it usually becomes gradually 

 withdrawn towards one side of the wall of the cell where it 

 becomes attached by its viscid investment to the primordial 

 utricle, but always forms the centre of the currents of sap. 

 The circulation of the protoplasm is very slow. I determined 

 it in the hairs of the filaments of Tradescentia on an average 

 of l-500th of a line per second." He gives the details of the 

 mode of circulation of the sap in the cells which are familiar 

 to all. After noticing that the nucleus and the protoplasm 

 gradually diminish with the age of the cell and the circulation 

 stops, he gives exceptions in which it is retained by the full- 

 grown cell, e.g., the stinging hairs of the nettle, the hairs of 

 curcubitaceous plants and of the filaments of Tradescentia, &c. 

 In those, active vital functions persist and we see the proto- 

 plasm remains in its integrity. Speaking of the apparently 

 ^ell-like appearance of the vacuoles in the protoplasm he indi- 



