394 ROYAL SOCIETY OF CANADA 
canals, thin-walled thyloses filled with protoplasm and starch began to 
make their appearance. It is thus seen that here also the canals are 
formed during the early stages of growth, when all the tissues are in a 
formative state, and that they occur mainly in regions manifesting very 
active growth. 
‘This concludes the description of the phenomena as observed in 
Pteris aquilina, and an account will now be given of other members of 
the Pteridophyta, which present similar appearances. The account of 
the latter, however, will be much less exhaustive on account of the lack 
of material showing the various stages. Nevertheless, these partial ob- 
servations will be of considerable aid in explaining the origin and func- 
tion of the whole structure 
In addition to Pteris aquilina two other Polypodiaceæ were exam- 
ined :— Onoclea sensibilis and Asplenium spinulosum. In Onoclea, 
fronds which were still in the bud stage, young fronds, and the rhizome 
were investigated, whilst in Asplenium only the base of the mature stipe 
was available. 
The buds of the fronds showed the various tissues to be in a form- 
ative state, the xylem being very thin-walled and rich in contents. The 
protoxylem groups were either intact or just beginning to split away to 
form a canal, which is in agreement with the appearance noted in the 
buds of Pteris. 
In the young fronds thyloses were observed, these standing out very 
clearly (Photo 13). They are much, larger than the surrounding cells, 
thin-walled, and full of granular cytoplasm. In no case were they seen 
to fill the canal completely in transverse section, and here and there 
rings and spirals of the disorganised protoxylem were visible in the 
cavity. 
Thyloses were also present in the rhizome, and are distinguished 
from the surrounding cells by their greater size-and by the more trans- 
parent and granular nature of their contents. As in the case of the 
parenchyma cells in this region, they act as reservoirs for the storage of 
reserve food in the form of starch. 
In sections of the mature stipe of Asplenium spinulosum taken 
at the base, each of the strap-shaped bundles had two groups of thyloses, 
one at each end. The thylosal cells here are very rich in contents, mainly 
starch. 
Of the Cyatheaceæ, Cibotium regale and Cyathea medullaris were 
investigated. 
The rachis of Cibotium regale was the only part available and 
showed the thyloses beautifully. In this organ there is only one large 
bundle which is horse shoe shaped with the free ends bent in. The xylem 

