406 McNicoL — On Cavity Parenchyma and Tyloses in Ferns . 
In Dicksonia antarctica the extent of a single strand is much the same 
as in Alsophila , though sometimes a little narrower ; but the cells themselves 
are considerably smaller, as shown in Fig. 7 in the plate ; and whereas 
in Alsophila a transverse section frequently shows only one very large cell 
representing the whole strand, in Dicksonia a similar section will show 
several smaller cells. Figs. 6 and 7 are drawn with a camera lucida to the 
same scale. In Dicksonia the cells are lignified and rather small, in 
Alsophila they are unlignified and large. In Hemitelia , which I examined 
only as dried material, the cells were arranged as in Alsophila ) the strands 
in the two being almost exactly the same width and generally one cell 
wide. In Cibotium princeps (Cyathea princeps , Hook.) a strand is generally 
Text-fig. 6. Transverse section 01 Text-fig. 7. Transverse section of a single 
petiole of Alsophila excelsa showing the form ‘bay’ in the vascular bundle of A. excelsa , 
of the vascular bun showing cavity parenchyma cp : the protoxylem 
px is not entirely destroyed. 
two or three cells wide and is about half the width of the bundle : the 
phloem immediately opposite the protoxylem is almost entirely displaced 
by the growth of the cavity parenchyma. Fig. 8 shows a transverse 
section of a portion of a bundle of C. princeps. In this species the tissue 
showed an even greater development than in the other Tree Ferns men- 
tioned, and showed, moreover, an interesting point which I have noticed 
in no other Fern. Most of the cells of the cavity parenchyma are thin- 
walled and of the usual nature : others, on the contrary, are reticulately 
thickened and lignified, and have all the appearance of water-storing 
tracheids. They resemble the ‘ Speichertrache'fden ’ described by Haber- 
landt (’ 96 ). In almost any transverse section, providing it was not too 
thin, these lignified cells could be seen. Some of them are very large, being 
about a quarter or a third the width of the bundle itself, thus forming 
a very prominent feature. Fig. 8 shows three of these tracheids and Fig. 9 
shows an enlarged view of part of the same preparation ; at px is seen the 
protoxylem, and at px 1 the spirally-thickened portions of some of the 
