390 ROYAL SOCIETY OF CANADA 
In figure 19 a canal is shown which has a fairly large lumen, filled 
to a considerable extent with the remnants of the disorganised proto- 
xylem. No thyloses are apparent. Figure 20 represents a similar 

Fig. 19.—Pteris aquilina. Rhizome. Canal, C., filled with remnants of the 
disorganised protoxylem, A.tr., Sp.tr. 490. 
canal but besides the disorganised spiral and annular tracheids, there 
is a large thin-walled thylose which is rich in protoplasm, the nucleus 
standing out clearly. 

Fig. 20.—Pteris aquilina. Rhizome. Canal, C., in a mature rhizome with 
thylose, Th., growing out into the cavity. X 490. 
Figs. 21 and 22 are representations of the same canal, but the former 
was obtained at a slightly lower focus. In this canal all stages of thy- 
lose development are observable in a region about 4 em. in Jength— 
from the first signs of thylose formation, as exhibited in the bulging 

Fig. 21.—Pteris aquilina, rhizome. Canal, C., showing thyloses, Th., of dif- 
ferent ages in same region. X 490. 
out of some of the parenchyma cells surrounding the canal (Fig. 22)— 
to the extreme case where the thylose presents a thick, higly lignified, 
reticularly marked wall (Fig. 21). The only inference that can rea- 

