PROTOPLASM THROUGH THE WALLS OF VEGETABLE CELLS. 
839 
In this direction I found that the method was in every way peculiarly adapted to 
show the intimate structure of sieve-tubes. In the course of my investigations on 
pulvini I had frequent opportunities for observing sieve-tubes, e.g., in Mimosa, 
Robinia, &c. In both the above-named cases the sieve-tubes are very small, but 
treatment with sulphuric acid, and subsequent staining with methyl violet and 
glycerine, or Hofmann’s blue, brought out these structures very successfully, and 
defined in an extremely clear manner the very fine threads connecting the contents of 
neighbouring tubes. The sieve-tubes of Dahlia variabilis, Ricinus communis, and 
Pho.seolus multijlorus were also investigated. In Ricinus the youngest sieve-cells 
where perforation had not yet taken place were clearly demonstrated. In Phaseolus 
the general occurrence of a lenticular highly refractive body in the sieve-tube cavity 
was noticed, but I must defer a description of it until a future occasion. 
But in the end the fact became apparent that although the results obtained with 
sieve-tubes gave very valuable proof of the success of the method I had adopted, yet 
that their structure could not be exactly compared to that of the parenchymatous 
cells of pulvini. Thus, in sieve-tubes, the cell-walls tend to assume a soft and some¬ 
what mucilaginous character, and in them the middle lamella is but little developed, 
and the whole wefil readily dissolves in sulphuric acid. 
In the cells of the pulvinus, on the other hand, the walls greatly resist the action 
of the acid, and the development of the middle lamella is essentially pronounced. 
There was, however, still one road left open, and that was to investigate the 
structure of thickened endosperm cells where all the requisite conditions were present, 
and what was of greater importance still, where the pit membrane was extremely 
thick, and would be likely to show plainly the existence of threads traversing its 
substance. 
Some results had already been obtained in this direction, for Tangl,* in 1880, in 
his paper on “ Open Communication between the Cells of Endosperms,” had shown 
that in Strychnos Nux-vomica, Phoenix dactylifera, and Areca oleracea, a communica¬ 
tion between the protoplasm of neighbouring cells was established by means of fine 
protosplasmic threads running through the cell-wall. In Strychnos the walls were 
thick and devoid of pits, and the presence of the threads was not confined to any 
particular portions of the cell-wall, but they occur over the whole area. In Phoenix 
and Areca, on the other hand, it was by means of pits that the connexion was brought 
about; the pit membrane being perforated in a manner very much resembling that 
which takes places in a sieve-tube. 
Tangl’s results with Strychnos were fully confirmed by Strasbtjrger, I but in the 
case of Phoenix and Areca, he states that he was unable to see the threads with 
the clearness conveyed by Tangl’s figure, and although he says that the pit 
membrane of Phoenix is demonstrably porous, yet the general tone of his statements 
t Loc. cit. 
* Loc. cit. 
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