THE VEGETABLE CELL. 39 



bility to be the case in the cells of many succulent fruits, in which 

 the nucleus frequently remains perfect up to the time of the ma- 

 turation of the fruit. In one series of cases, however, the circu- 

 lation is persistent in the full-grown cell, e. g,, in the stinging hairs 

 of nettles andioasc^, in the hairs of Cucurbitaceous plants, in the 

 hairs of the filaments of Tradescantia, in the hairs of the corolla 

 of Campanula Medium^ in the cells of the leaves of Sagittaria 

 sagittifolia, Stratiotes aloides. In some plants the protoplasm is 

 not distributed in isolated reticularly arranged currents, but flows 

 along the cell-wall in a broad stream, returning back upon itself in 

 a circulai^ direction at one side of the top of the cell, and flowing 

 down upon the other side, the nucleus following the current. This 

 form of the circulation is displayed very beautnuUy in the cells of 

 the leaves of Vallisneria spiralis, and in the cells of Chara, the 

 inside of which is clothed with spii^ally arranged rows of chloro- 

 phyll granules, which the current accurately follows. 



Ohserv, 1. The wonderful phenomenon, of the movement of the proto- 

 plasm is usually designated by the most unsuitable name of " rotation of 

 the celhsap." Although described by Corti hi 1774, the phenomenon 

 was altogether forgotten till discovered a second time by Trevn'anus in 

 Charcdj m. 1807. For a long time it was supposed to be a peculiarity 

 belonging to a few water plants (Charcb, Hydfocharis, Vallisneria^ Cavn 

 liniajj until the researches of recent times shewed that it was an univer- 

 sal phenomenon. The cause of the motion is altogether unknown ; the 

 explanation of Amici, that in Cliara the rows of chlorophyll granules which 

 clothe the walls of the cells, and wbich the current of sap follows, exer- 

 cise a galvanic action upon the sap, and thus give rise to the motion, can- 

 not be considered applicable, since these granules are absent in all other 

 plants and even in the roots of Ghara. The description of the pheno- 

 menon in question, by Schultz, fm^nishes a pattern of imperfect observa- 

 tion and unfortunate conclusions ; he regards the currents of protoplasm 

 as composed of milk-sap, flowing m a branched vascular system, having 

 its origm in the vessels of the milk-sap, and penetratmg the walk of the 

 cells ("D^e Cyclosis des Lebensajtes in der FflanzeP 293). 



OUerv, 2. According to Schleiden's statement {^'^Grundzp i. 211, pi. 1, 

 fig. G), it sometimes happens that a secondary cell-membrane becomes 

 deposited over the nucleus as it lies upon the wall of the cell, so that it is 

 enclosed in the substance of the cell-membrane and protected from fur- 

 ther change. This account is altogether incorrect. The nucleus, like all 

 the rest of the contents of the cell, lies in the cavity of the primordial 

 utricle, and the cell-membranes are formed over the outside of the latter. 

 The conditions which determine the early solution of the nucleus or its 

 persistence in the full-grown cell, are altogether unknown. ^ It vanishes 

 very soon in vascular utricles and in wood-cells ; it has likewise veiy often 

 disappeared from fall-grown parenchyma-cells, especially in those of the 

 middle layers of the stem, while it is very frequently found quite perfect 

 in spores, pollen-grains, in the cells of jomted hairs, in the cells of berries, 

 and in the boundary cells of stomates ,• the cellnlar tissue of many Or- 

 chldese and Commelynacese is remarkable for the long retention of the 

 nucleus. 



