404 McNicol — On Cavity Parenchyma and Tyloses in Ferns. 
a cell-wall ; Fig. 5 shows a series of three swellings in three distinct vessels, 
all formed from a single cell and not separated by cell-walls. This is quite 
common in Nephrolepis which shows perhaps better than any fern the 
tylose-like nature of the cavity parenchyma. The cells may eventually 
become cut off by cell-walls. 
In Strutkiopteris pennsylvanica , one of the Aspidieae, the petiolar 
bundle is much elongated and the cavity parenchyma is only slightly 
developed ; it can be seen adjoining the two groups of protoxylem near 
the ends of the bundle ; at these points the sheath cells were slightly 
enlarged, and remains of the disintegrated vessels were to be seen between 
them. In longitudinal section some of the cells are seen to be crenulated 
Text-figs. 2, 3, 4, 5. 
Text-fig. i a. Diagram of petiolar Stages of formation of cavity parenchyma in 
bundle of Nephrolepis. Nephrolepis. 
E, endodermis. XY, metaxylem. 
PH, phloem. 
in outline on the side adjoining the spiral vessels, but the development of 
the tissue is not striking. 
In Aspidium Filix-mas , in which the bundles are numerous and 
more or less rounded in form when seen in transverse section, and the 
vascular elements are narrow, there was no trace of cavity parenchyma, 
but longitudinal sections showed a slight bulging of a few sheath cells, 
though no actual ingrowth to the vessels was to be seen. In the petiole 
of Sadler ia cyatheoides a Fern of tree-like habit, which I examined 
as dried material only, the cavity parenchyma was slightly developed. 
In Lomaria gibba, a form having small round bundles, the parenchyma 
was distinct in some bundles and not to be seen in others in the same 
cross-section. The cells were about the width of one of the wide 
tracheids of the bundles. There was no cavity parenchyma in Asplenium 
Ruta-muraria, but one or two cells were to be seen which had apparently 
enlarged, and slightly crushed an adjoining spiral vessel. In the sub-order 
Pterideae I examined Pteris aquilina , , Gymnogramme ochracea , and Chei- 
lanthes pulverescens , in the first of which cavity parenchyma was recorded 
by Terletzski (’84), as mentioned above. It is also present in the two last- 
mentioned Ferns. In Pteris the tissue is more striking than in Gymnogramme ; 
