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ROYAL SOCIETY OF CANADA 
4.—Pteris aquilina, stipe, May 29th, 1899. Canal showing thyloses be- 
ginning to form from the bounding wood parenchyma. X 230. 
5.—Pteris aquilina, stipe as above. Canals showing lysigenous formation 
and protoxylem rings bordering the cavity.  X 230. 
6.—Pteris aquilina, stipe as above, posterior end. Canal filled with nucle- 
ated thyloses.  X 230. 
7.—Pteris aquilina, stipe, Oct. 25th, 1906. - Showing thylose modified to 
form a vessel and surrounded by an irregular epithelium. XX 230. 
8.—Pteris aquilina, stipe, Oct. 25th, 1906. Thylose modified to form a 
. vessel and surrounded by a perfect epithelium. X 230. 
9.—Pteris aquilina. Same group of thyloses as in Photo 9, but in an- 
other section. Showing the change in the regularity of the epithe- 
lium. X 230. 
10.—Pteris aquilina, stipe, Oct. 25th, 1906. Mature canal blocked by 
thyloses. XX 230. 
11.—Pteris aquilina, Rhizome. Showing the position of the canals with 
thyloses in the vascular bundle. X 52. 
12.—Pteris aquilina, Rhizome. Showing unbroken protoxylem in a bundle 
of slow growth. X 200. i 
13.—Onoclea sensibilis, young stipe. Canal filled with young thyloses. 
* 230: 
14.—Cibotium regale, stipe. Thylose modified to form a vessel and sur- 
rounded by an epithelium. XX 230. 
15.—Cyathea medullaris, rachis. Canal filled with large thyloses. X 230. 
16.—Todea barbara, very young stipe. Showing the protoxylem in the 
position of the later thyloses.  X 200. 
17.—Todea barbara, mature stipe. Showing thyloses filling the canal 
which arose in the position of the protoxylem. X 200. 
18.—Osmunda regalis, stipe. Showing young bundle with the protoxylem 
in the place of the thyloses in the older bundles.  X 52. 
19.—Osmunda regalis, stipe. Thyloses in older bundle in the position of 
the earlier protoxylem. X 230. 
20.—Angiopteris evecta, rachis. ‘Two groups of thyloses in a vascular 
bundle. X58. 
21.—Botrychium virginianum, stipe. Thyloses with prominent nuclei and 
protoxylem floating in canal. 280. 

