Development, and Structure of the Vegetable Cell. 29 
the cell, where the primary cell-membrane is still adherent to the 
secondary. 
If a vigorously growing Spzrogyra, after the first operation of 
the diosmotic fluid has effected the complete separation of the 
secondary cells from the membrane of the primary, be laid in 
pure water, the secondary cells, with their contained tissue of 
cells, appear to regain their former position. 
If the diosmotic fluid be allowed to effect a complete contrac- 
tion of the secondary cells, and the surrounding liquid be then 
rapidly replaced by pure water, the secondary cells do not again 
expand (either from the entire exosmosis of their contents or 
from the rupture of their walls), but the non-nuclear daughter 
cells (vesicles) then break through the membrane of the second- 
ary cell and progressively expand, the larger of them usually 
again entirely occupying the cavity of the mother cell, and 
proceed to form a septum at the middle by the juxtaposition of 
their walls. 
In this case the same phenomena occur as mechanical effects 
which have been observed as the normal process of growth in 
the continuously developing daughter cells of Gidogonium. If 
the experiment be made with Spirogyre in a state of vegetative 
repose, in which the endogenous cells are less developed and do 
not entirely fill the mother cell, then, during the exosmotie con- 
traction of the secondary cell, its membrane is torn completely 
across in the middle of the two enclosed daughter cells, together 
with the portion of the chlorophyll-sac which is here situated. 
Under such circumstances, moreover, the daughter cells, after 
the addition of the water, protrude from the spiral sac and those 
portions of the envelope of the mother cell that covered them, 
and proceed to expand in the manner described, constituting 
that condition which has hitherto been erroneously supposed to 
originate from fission of the secondary mother cells (figs. 78 & 
79, from S. guinina). 
These different diosmotic reactions exhibited by the several 
nested cells within a joint-cell are probably dependent on the 
different nature of their membranes, as indicated by their dif- 
ferent degrees of thickness and firmness, and probably also on 
the varying quantity of their component elements, which are 
cognizable by no chemical distinctions. 
Both the primary and secondary cells of a joint-cell, and also 
the non-nuclear transparent daughter cells, contain a material 
which is coloured blue like starch by an aqueous solution of iodine, 
after maceration not only with dilute solution of sulphurie acid 
or chloride of zinc, but also with a neutral solution of chloride 
of calcium. In this state it is commonly more or less slightly 
turbid, hike finely divided starch. The contents of the primary 
