IV. On tho continuity of the protoplasm through the wall» of vegctable cclls. 63 
such a strong reagent as Sulphurie acid great displacemenl of the tissue is 
li.ilde lo occur. Laslly and most imporlanlly the direction of the long axes 
<>f the pits, and consequently of the protoplasmic processes lie in all planes, 
and it is obvious thal rnany processes whieh lie in a plane inelined even at 
a very slight angle lo the plane of the coverslip will appear lo touch one 
another and be continuous, although as a matter of fact thcy may be sepa- 
i'aled by a considerable space. Consequently the greatest precautions must 
be laken. All exlraneous light should be kept from the eyes and il is best 
to work wilh the microscope under a wooden screen made for the purpose 
W'hich admils light lo the mirror only by nieans of a hole cut in the front, 
ßy careful observation one must learn to recognize exaclly the eflects whieh 
Hie acid produces, and the whole phenomena atlending the swelling of 
tissues. It must be remembered that the middle lamella completely sur- 
i'onnds each cell, and that in a seclion the network of lamellae occur in all 
planes, and that the various constituent lamellae appear lo intersect one 
another at all angles. In the examinalion of the processes and of the inter- 
cepling closing membranes the greatest possible care must be laken to 
acertain that the long axis of the particular pit in vievv lies as nearly aS 
possible at right angles to the line of vision, or whal is the same thing, lies 
in a plane parallel lo the plane of the coverslip. 
1 will now deal wilh the various resemblances whieh as I have slated 
simulate an actual occurrence ol a protoplasmic continuity. As to the ap- 
pearance ol a somewhat thick thread bodily traversing the junction between 
two opposite pit-cavities and necessilating the idea of open pits, it can be 
easily shown that it is fallacious, for thin sections either of fresli or alcoholic 
material, stained wilh Jodine and mounled in Chlor-Zinc-Jod. demonslrate 
that in every case a closing membrane is present, and that the ends of the 
two opposite processes are sharply defined from it. Such an appearance is 
due either lo the fact that the plane of the long axis of the pits is inelined 
at an angle to that of the coverslip, or that the pil-membrane has not been 
swollen, and since it is very thin, slightly stained, and at the same time 
in the thicker sections difficult to dehne, it appears at first sight as if no 
pit-rhembrane were present, but a careful examinalion w ill generally enable 
one to see that an intercepting closing membrane is in reality present in 
all cases. 
Wilh regard to the fine processes appenring to perforate the closing 
membrane it is obvious that Ihis necessilales the exislence of a small pore 
in that slructure. But by the most careful examination of pit-closing-mem- 
branes I have failed to delect the exislenc§ of any such Perforation, and as in 
•nany instances the threads are of an appreciable size lliey such a Perforation 
°i fbe pil-membrane ought cerlainly lo be recognized. On the contrai s in 
die whole ol my work on endosperms and olher tissues liiere was no single 
‘nstanee of such a simple Perforation, but a sieve arraugement was present 
