[KIRSCH] CERTAIN STRUCTURES IN THE PTERIDOPHYTES 387 
stränge appear to be widely present in the ferns, but have been very little 
noticed up to the present.” 
From the description it is clearly evident that Terletzki had no 
idea of the nature of these structures. He considers the lacunæ to owe 
their origin to the mode of apposition, or to the irregular shape of the 
constituent parenchyma cells, which he regards as a peculiar form of 
the ordinary wood parenchyma. 
He now proceeds to give a brief historical account of former refer- 
ences to these structures, and, as some of the works he cites were inac- 
cessible to the writer, it will be well to reproduce certain passages in 
toto, especially since they are very brief. 
“Dippel figures such a strand of cells from Osmunda regalis 
(4, pp. 201, 202), (5) and Cyathea microlepis (5) and describes it as 
follows :— 
“In the frond of several tropical (Cyathea, Asplenium), and in 
isolated forms of domestic ferns (Osmunda, now and again Pteris), 
there are to be observed strands of peculiarly built, (ausgebildeten), 
parenchymatous cells, which are apparently set aside for the reception 
of secretory products and which are to be placed side by side with the 
resin, gum, and lactiferous passages of the phanerogams. These appear 
on the side of the bundle which curves inwards, either singly, or, in the 
case of longer drawn out bundles which are strap-shaped in cross section 
(Osmunda), at several points. The component cells are mostly irre- 
gularly polyhedral or roundish, of wide lumen, and filled here and there 
with a yellowish, oily to resinous mass. They possess a wall which is 
either very little thickened, or rather strongly thickened and with pitted 
or reticulated markings.” 
From this it can be seen that Dippel regarded these cells as por- 
tions of the parenchyma specialised for the storage of different secre- 
tions, such as resin, ete. But although, as will be shown later, special- 
isations which no doubt tend to the formation of such reservoirs, are ob- 
served in certain stages of Pteris, still they are not definite enough to 
be called such. However, as far as can be seen from the context, Dippel 
probably confused certain mucilage, tannin, and resin bearing cells in 
forms like Osmunda and Todea with the thylosal growths under dis- 
cussion, for in these forms the mucilage, etc., bearing cells alternate with 
the thylosal structures and at certain stages resemble them in practically 
all respects. Thus, unless observed at different stages of growth, it is 
very difficult to differentiate them except by their respective positions 
in the vascular bundle. 
