THE STRUCTURES OF PITOHER PLANTS. 267 
without being included by the epithelium, and then I give to them the 
name of ostioles. On the pedicels of the Droseracess they are seen to be 
»apillary in some instances. (Fig. 5.) These ostioles never have air 
bubbles in them as the stomata invariably have, unless they have been 
removed by maltreatment; and they are smaller than stomata, being 
"035mm. in their largest measurement, whilst the latter are almost 
uniformly :05. Cells do not radiate from stomata as they do from 
ostioles. Their relations to other parts, their special distribution, and 
the fact that I have seen their contents undergo changes when the 
fragment of leaf has been bathed in a solution of phosphate of ammonia, 
and once in the case of Drosera intermedia, when the leaf was bathed in 
_a solution of peptone, the result of digestion in a Nepenthes pitcher, 
make me certain that their function is the absorption of the food of the 
plant. 
Another variety of epithelial absorbentis the tubular trichome found 
in certain pitchers. It is always associated with a system of intercellular 
canals, and seems really to be developed from the protoplasm contained 
in these canals more than from a cell, the cell wall apparently going to 
constitute the lining membrane of the tube, its protoplasm disappearing. 
At the upper side of the margin of the base of the trichome its proto- 
plasm can be seen to be continuous with that of the intercellular canals; 
and in the growth of the hairs this can be seen to be deepening in colour 
and increasing in quantity at the lower part, so as to form the process of 
the trichome. This observation can be best made at the lower part of 
the fourth zone of a young pitcher of S. purpurea (Fig. 6.) At the free 
extremity of these tubular trichomes there must be a true stoma, though 
I cannot pretend to have seen it. But I have seen a bubble of air enter 
at the extremity of the tubule, and I have traced its slow passage, coin- 
cident with the shrivelling of the fragment examined; and the air 
bubbles may be made to alternate with short columns of water by alter- 
nately wetting and drying the surface. 
The systems of intercellular canals to which I have referred are 
best seen on such surfaces as absorb digested food. Thus on the inner 
surface of a Nephenthes pitcher examination by high powers will 
demonstrate these canals beyond dispute. They are walled and contain 
protoplasm, for its columns may be seen broken at irregular spots. They 
are undoubtedly absorbents, for I have repeatedly satisfied myself that 
they were larger in pitchers which had been fed, had digested and were 
absorbing their food, than they were in virgin or starved pitchers of the 
same plant; and the fact that the tubular trichomes of Sarracenia are 
developed from the protoplasm contained in these canals is a further 
argumentin favour of this view. The most complete proof of the actual 
existence of these canals is to be obtained from diseased epithelial 
surfaces where fungous growth is found to be extending into them from 
an ostiole and distending them. In several pitchers of S. flava and also 
of S. rubra, I have found the ostioles so infected that their characteristic 
protoplasm had been destroyed, but their canals were so dilated that the 
connecting systems between the ostioles could easily be traced and 
