378 ROYAL SOCIETY OF CANADA 
ones typical of the stipes that have been discussed above. In these long 
bundles as many as ten or twelve patches of thyloses are evident in trans- 
verse section, and some of these patches are very large, frequently con- 
sisting of from 20 to 40 cells of different sizes. In some of the smaller 
bundles the region filled with thyloses is so large, that it extends through 
the whole parenchyma region on the concave side of the horseshoe-shaped 
xylem and adjacent to it. This fact leads to the conclusion that the 
canals in these bundles were very large, which would be in accord with 
the vigorous growth these large stipes must have exhibited when their 
various tissues were in a formative state. 
The thylose cells themselves are often thick-walled, and rather poor 
in contents, their lumens usually exceeding those of the surrounding 
parenchyma cells several times. The thylosal groups are frequently so 

Fig. 7.—Pteris aquilina. Stipe, Oct. 25th, 1906. Showing thyloses, Th., with 
broken protoxylem rings and spirals, Sp. tr., A.tr. X 367.5. 
clear of contents that they present the appearance of a large irregular 
canal with partitions crossing it in various directions. This appearance 
is heightened by the fact that disorganised protoxylem elements, which 
seem to lie in the cavities between the partitions, are generally visible. 
As a rule there are a number of larger thyloses in the centre of 
each group, with smaller cells at the periphery, the outermost ones closely 
approximating the adjacent parenchyma cells in size (Photo 10). The 
cells frequently overlap one another, and this is well illustrated in figure 
7. This figure also shows a small portion of the original canal, C, which 
