96 ON THE PLANT-CELL. 



isolated, and filled with a colourless clear fluid. At one part of the wall is 

 affixed a sharply defined, faintly granular cytoblast, presenting a well- 

 marked nucleolar corpuscle. The cytoblast is always surrounded by a 

 narrow areola of a yellowish mucous fluid, thickly crowded with minute 

 opaque granules, and from it proceed currents of various width and 

 depth. At the margin, and consequently where the cell is viewed from 

 the side, these currents are often seen to advance with distinct minute 

 undulations: the direction of some of the currents is from the cytoblast, 

 of others towards it. In their course they exhibit numerous branches, 

 and anastomose with each other : in these plants only rarely, but in others 

 more frequently, separate currents traverse the cell, in order to unite 

 with other currents on the opposite side. Many of the streams are so 

 minute, that under the highest magnifying power they exhibit the 

 appearance of a line without any breadth, merely rendered to a slight 

 extent irregular by the individual granules. Occasionally a current is 

 suddenly interrupted, the leading portion continuing its course; a minute 

 drop of the fluid is then formed at the extremity of the remaining portion, 

 from which, after some time, the current is continued in the former or 

 in a new direction, or else two or more currents proceed in a new direc- 

 tion. In this respect, all other cells present merely unessential differ- 

 ences, of which, however, the most interesting is exhibited in Cerato- 

 phyllum* There are certain facts that must be borne in mind, in future 

 attempts at explaining the nature of the motion described in the two 

 preceding paragraphs, and which may probably lead to the explanation 

 of them : these are the endosmosis and exosmosis, which must neces- 

 sarily, in some way or other, give existence to a motion of the cell 

 contents; the continuous formative agency of the cytoblast, the pecu- 

 liar nature of the circulating fluid, its immiscibility with the watery 

 sap, its great adhesion to the cell-walls, as well as its great intrinsic 

 cohesion. At present it must be confessed, however, that we are not in 

 a condition to construct any useful theory out of these elements. 



As far as it can be determined with certainty, the circulating fluid 

 appears invariably to be mucus (albumen?). When cells, in which is 

 exhibited the circulation described in this and the preceding section, are 

 submitted to the action of alcohol or nitric acid, the mucus contracts on 

 its coagulation, and may be observed to invest the whole surface of the 

 walls with a thin layer, and the currents will be seen to constitute merely 

 thicker streaks of mucus. The same thing takes place in every cell as 

 yet immature. Both in the latter, and in those cells which exhibit a 

 circulation, the cell-contents frequently coagulate of themselves, in con- 

 sequence of chemical processes in the cell, and then retract spontaneously 

 from the walls. In cells undergoing lignification the mucus gradually 

 disappears. In all young cells the mucous investment may be de- 

 monstrated also by the use of iodine. Might not its existence be 

 said always to indicate motion ? What phytotomist can have over- 

 looked the innumerable instances of cells in which mucous filaments 

 radiate from the cytoblast ? Whenever I have examined these cells in 

 the earlier condition, I have never failed, with due perseverance, to ob- 

 serve the circulation in these mucous filaments, or rather streams. The 

 mucous layer in question is frequently so little granular, that its motion 



* See my " Beitrage zur Kenntniss der Ceratophylleen in the Linnaea," vol. ii. 

 (1837), p. 527, et seq. Botanische Beitrage, vol. i p. 213, et seq. 



