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 mimutes. 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 insufficiently 
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 m which the 
cellular contents of the Conferva are lying a watery solution 
of iodine or tannin, the phenomena of distention and bursting 
