320 SIGNOR U. MARTELLI ON THE CAUSE OF 
of successive changes, for which reason the continuity and the 
resistance of this tissue diminishes. 
Thus, under these circumstances, even a very little effort 
will occasion the separation of the cells. So that, in conse- 
quence of the irritating action caused by a stroke given to the 
plant, the sepals at once rise up, becoming connivent, and by 
this movement they press against the corolla, which, by the 
decreased cohesion of the cells of the separating zone, easily 
separates and is thrown off. But, to explain this phenomenon 
more clearly, let us divide it into two periods, and consider 
the sepals as consisting of two parts—the base and the lamina. 
In the first period it is the base of the sepal which acts, 
and closes against the corolla in such a way that it compresses 
the base of the corolla, and obliges it to slide forward, and 
thereby separates it from the thalamus. By paying close 
attention to this period, we perceive in the corolla at first 
a slow forward movement, which probably corresponds to the 
separation of the cells of the separating zone, and in the second 
place a slighter, but at the same time abrupt movement of the 
corolla, which certainly happens when the vascular bundles break. 
During the second period the lamina of the sepal rises, with a 
more or less rapid movement, and, leaning against the corolla and 
compressing it, pushes it continually forward until, owing to its 
weight, it gradually falls off. Then the sepals continue the con- 
verging movement till they completely enclose the ovary *. 
In the same way, the base of the small tube of the corolla 
seems to me to have a structure which facilitates the expulsive 
action of the calyx. This is the way that Verbascum Blattaria 
is formed :—In the lower and external part of the tube of the 
corolla we notice an unexpected swelling, with a pentagonal 
outline, almost as if it were a protruding ring (fig. 2, a). From 
the external border of this ring to the circular orifice of the 
corolla, the very short part of the tube (fig. 2, 6) is very smooth, 
* In some species, as for instance in Verbascuim floccosum and Verbascum 
sinuatum, when the corolla has fallen, the sepals become at once connivent 
with a rapid movement. In other species, as for instance in Verbascum Blat- 
taria, this movement is slower, and some time is necessary before the sepals 
assume their final decisive position—that is to say, perfectly connivent. I have 
also severed the sepals, so as to ascertain their expulsive action; but I cannot 
add anything to what I have already said, unless it be that they have confirmed 
me still more in the opinions expressed. 
