66 
Walter Gardixer. 
this stage to that of complete clearness of structure where the threads may 
even be counted, the tissues of various endosperras give many examples 
and offer every gradation. Moreover when those which with a high power 
exhibit well detined threads, are examined under a low power of the micros- 
cope, they present exaclly the sarne appearance as Mimosa, the stained area 
has the sarne ligure of a compressed sphere in the closing membrane, and 
the threads which can no longer be distinctly recognizcd, give an appearance 
of striation or only a mere colouration. Every peculiarity in the structure 
of the endosperm threads, such as that frequentlv disjdayed in the pe- 
culiar sweep of the threads, giving rise to a much flattened spheroid 
lorrn, are all faithfully reproduced in the tissues of pulvini and the like. 
These eonsiderations and results, which will become even more evident afler 
I have dctailed my work with endosperms, will I think prove that a sieve- 
structure does prevail, and that it is moreover the only true rneans whercby 
a protoplasmic continuity is established in Mimosa. The fact of protoplasmic 
continuity is also very greatly supported by the wonderful adhesion of the 
protoplasm to the base of the pit-membranes. With Chlor. Zinc. Jod., at 
least as far as regards Alcoholic material, the tissue of the pulvinus of 
Mimosa swells but little, and after such treatment the evidence as to the 
presence of protoplasmic lilaments traversing the closing membrane is limited 
rnerely to a definite staining of that structure.') 
After swelling with Sulphuric acid the pulvinus of liobinia displays 
essenlially the sarne structure as that of Mimosa; but there are much clearer 
examples of a sieve-arrangement, for the stained area connecting to neigh- 
bouring protoplasmic processes, shows a much more evident striation. In 
Amicia on the olher hand 1 was unable to observe any appearance of stria¬ 
tion, but only a uniform and apparently structureless stained area. In 
Phaseolus also the evidence as to continuity is limited to a mere staining of 
the pit-closing-membrane. 
It is also of extreme interest to note that the degree of tenacity with 
which the apices of the processes cling to the pit-closing-membranes in the 
various examples I have named, benrs some very definite relation to the 
degree of development of the threads Crossing the pit-closing-membrane. 
Thus in Mimosa the processes projecting inlo the pils continue to stick 
to the pit-merabrane even though the tension upon them, as exhibiled bv 
their extreme tenuity, is very great. In many instances indeed they stick 
so closely to the membrane as to produce every impression of the existenco 
of a direct continuity between the cells; and w hen, ow ing to the protoplasm 
having undergone considerable shrinking, such a tension has been brought 
to bear upon them that rupture finally ensues, such rupture, in a very great 
l) I was unable to detect any diffcrence between the appearance presented by tho 
upper and lower sides of the pulvinus of Mimosa. 
