CELL-FORMATION. 101 



is the producer of the proper spore-cell. " I suspect that 

 Schleiden has observed a peculiar and enigmatical cell- 

 or utricle-formation, which occurs in Spirogyra, and of 

 which I shall hereafter take especial notice. This cell is 

 neither the rudiment of a germ-cell, nor the germ -cell 

 itself, nor is it produced from the nucleus of the cell. It 

 appears to me that the cell-nuclei which lie in the centre 

 of the cells of Spirogyra do not play any important part 

 in the origin of the cell. They are often visible until the 

 cell-contents accumulate into a ball, then they disappear ; 

 but they are by no means hidden in the contents, since 

 if they are still visible in the later stages, they are on the 

 surface of the green contents. I have therefore no doubt 

 that the nucleus of the parent-cell becomes dissolved 

 before the contents are transformed into a germ-cell. 

 Besides, it is not evident what two nuclei should do in 

 the formation of one cell, each conjugating cell having 

 one nucleus. In pi. II, fig. 5, some cells of Spirogyra 

 quinina are figured, in which germ-cells are formed with- 

 out conjugation. In two of them the nucleus is seen on 

 the surface of the contents ; in the third it has dis- 

 appeared. 



I mentioned also another free cell-formation, without 

 visible nucleus, where the observation in like manner 

 affords a tolerably certain conclusion. This is the origin 

 of the sporangia in AcUya prolifera. I have already 

 alluded to this point in the first part of this essay,* in 

 reference to the so-called division of cells. Aclilya furnishes 

 remarkable facts, both on parietal and free cell-formation, 

 so that I will give some figures of it. In the clavately 

 swollen ends of a branch are formed usually one, more 

 rarely two or three sporangia. If there be two or three 

 (PL III, figs. 5 and 6), these originate by free cell-for- 

 mation ; if there be merely one, it originates sometimes 

 through free (fig. 3), sometimes through parietal, cell-for- 

 mation (fig. 7). When the sporangia originate by free 



* Ray Society's Translation, p. 279. 



