PROTOPLASM THROUGH THE WALLS OF VEGETABLE CELLS. 
849 
nearly so great, and this fact both increases the difficulties of making out the threads, 
and in consequence of the rapid blue coloration of such a thin membrane causes the 
observations with iodine and Chlor. Zinc Iod. frequently to be almost valueless and 
often an impossibility. It is in such cases that my staining method comes to be so 
important. 
Often it would seem that the threads are so excessively fine that they cannot be 
resolved as separate filaments, and the appearance presented by the whole aggregate 
of threads crossing the pit membrane is simply that of a blue coloration. In this 
direction the results with Bomarea are of special interest, as they tend to give weight 
to the view that my experiments have led me to adopt, viz. : that a well defined blue 
coloration, after the action of Chlor. Zinc Iod. and picric-HoFMANN’s-blue, points to 
the presence of protoplasmic threads in the cell-wall. 
Professor Strasburger * states, in the case of the endosperm cells of Ornithogalum 
and in the pith cells of Taxodium, that the pit membranes are demonstrably porous, 
and that a striation can be observed crossing the membrane upon action with iodine 
and Chlor. Zinc Iod. He also represents this striation in figs. 17, 18, 19, and 23, 
Tafel I. ; and again in fig. 23, Tafel II., he shows that a similar striation may be seen 
in the closing membrane of the pits in the thickened cells of the seed-coat of Viscum. 
As far as regards Ornithogalum I can fully confirm his results, and the fact of the 
existence of a similar structure in Taxodium and Viscum is one of great value. 
Staining with picric-HoFMANx’s-blue, subsequent to the action of iodine and 
Chlor. Zinc Iod., will demonstrate in the case of Ornithogalum that the pit membrane 
is distinctly blue, while the rest of the cell-wall is practically colourless, and will also 
bring out more clearly the striation of the pit membrane, due to the presence of 
threads. This, however, is by no means a favourable case. 
Sections of the endosperm cells of Bomarea oligantha, after swelling and staining, 
gave me good results. If examined in a somewhat cursory manner it is at once observed 
that the pit membrane is well coloured and distinctly delineated from the rest of the 
cell-wall (Plate 70, fig. 27). In some instances it can be observed that instead of 
the whole pit membrane being uniformly coloured, it may be traversed by one or two 
coloured bands which run through the otherwise colourless substance of the membrane 
(refer to figure). In favourable instances well defined striation can be seen. In an 
enface view of the pits it becomes evident that the pit membrane exhibits essentially 
the same appearance as that presented by a sieve-plate (Plate 70, fig. 28), and the 
appearance of the two coloured bands is explained from the fact that in some instances 
the whole membrane is not necessaiily perforated, but that the perforation and hence 
the sieve-plate structure may be confined to particular areas of the membrane of the 
pit. This particular distribution of perforating areas also explained the appearance of 
bifurcation, which is sometimes presented by the apex of much contracted protoplasmic 
* ‘ Bau und WacKs-tlrum,’ p. 10, et seq. 
