Development, and Structure of the Vegetable Cell. 415 



are very commonly met with enclosed within a larger and equally 

 delicate common cell-membrane. This outer wall, which lies at 

 first in close apposition with the inner cells, becomes, by the 

 imbibition of water, much removed from them, and, by the 

 longer operation of endosmose, gets so much stretched that it 

 becomes ruptured at some point, whereupon the hitherto smooth 

 and structureless membrane suddenly collapses, appears granular, 

 and proceeds to dissolve, commencing from the gaping margins 

 of the fissure. 



The vesicles and cells imbedded in colourless or greenish 

 mucus, set free by the dissolution of the mother cell, are now 

 likewise exposed to the action of the water, to which they yield 

 in just the same manner as the others, usually bursting in the 

 course of ten or fifteen minutes. If the water be only in small 

 quantity, the expanded membrane is preserved in the surround- 

 ing mucilage for some time longer. 



Former observers have remarked similar phenomena : as, for 

 example, Meyen, in the case of the gonidia extruded from joint- 

 cells ; Saulier, in those of Derbesia; Unger, in Achlya prolifera; 

 Itzigsohn and Hartig, the latter in Vaucheria dichotoma. Never- 

 theless they have all taken a different view of these insuflSciently 

 noticed facts ; for they have looked upon the mother cell cast off 

 from the daughter cells in the course of endosmosis (following 

 the hypothesis of Mirbel) as originally a secreted layer precipi- 

 tated around them. 



Hartig says that, upon cutting through a Vaucheria, cell-vesi- 

 cles may be seen emerging and separating themselves from it by 

 constriction, presently bursting and emptying a portion of their 

 fluid matter, and then, by the contraction of their integument, 

 closing again, and swelling up anew. Moreover he affirms that 

 two or more sacs which have been cut through may coalesce by 

 a sort of conjugation into a single vesicle. 



By repeated investigations respecting these phenomena, I have 

 convinced myself that these apparent detachments, contractions, 

 and repeated dilatations are nothing else than the successive 

 expansion and dissolution of an endogenous system of cells. 

 Those vesicles which have once burst or been cut through never 

 unite with one another or become again distended by endos- 

 mosis, as Hartig believed he had seen them do; but they undergo 

 a continuous breaking up. The uninjured superimposed cells 

 in close contact with each other are with difficulty recognizable, 

 on account of the great delicacy of their membranes, when their 

 contents are uncoloured, and consequently they appear to form 

 only a single cavity. By adding to the water in which the 

 cellular contents of the Conferva are lying a watery solution 

 of iodine or tannin, the phenomena of distention and bursting 



