THE FALL OF THE COROLLA IN VERBASCUM. 319 
centre. If we make use of iodine, the separating zone assumes 
a dark yellow colour. With fuchsin or iodine-green, even after 
many washings this tissue retains a beautiful red or green 
tint. On the other hand, if a section of a flower is treated 
with chloriodide of zine, the tissue of the corolla assumes a 
rather deep blue colour, the separating zone a light yellow 
tending to a green tint, and the underlying tissue of the thalamus 
remains uncoloured. 
The severance of the corolla from the thalamus occurs between 
the last row of cells of the separating zone and those of the 
corolla (fig. 1, 6). Therefore the stratum of smali cells, of which 
we have already spoken, remains adherent to the thalamus, as will 
be easily seen by dividing the two parts—that is, the corolla 
from the calyx—or by examining the thalamus just when the 
corolla has fallen off; the adherent tissue, which formed a part 
of the separating zone, dwindles and gradually disappears almost 
entirely. 
We will now refer to its antecedent condition, and take into 
consideration a flower still in the bud. The separating zone at 
this epoch is already visible, and the tissue appears opaque and 
of a yellowish colour: the chemical reactions obtained have 
already been noticed above. As to size, the cells of the separating 
zones are very little different from those of the corolla and 
of the thalamus, though smaller, but they have a pentagonal 
shape. Little by little, as the flower develops, the tissue of the 
separating zone assumes more of its character, the cells subdivide, 
their shape is modified, becoming gradually rounder in form. 
This variation of shape is, I consider, very important in the 
phenomenon of the fall of the corolla which we are considering, 
because, owing to this change, the corolla acquires less power of 
cohesion to the thalamus, as I will hereafter explain. 
Il. On the Fall of the Corolla. 
The power of resistance possessed by the flower when only in 
the bud-stage, or but just expanded, is, in my opinion, explained 
by the cohesion of the cells of the tissue of the separating zone. 
In the flower still in bud these cells are pentagonal, and for this 
reason they form a united and compact tissue, which offers more 
resistance; on the other hand, in the flower which has been open 
some time the cells become smaller and rounder, in consequence 
