98 Gwynne- Vaughan . — Solenostelic Ferns. 
sc. t ., sclerosed sieve-tubes; Ip , cavity-parenchyma opposite each of the proto- 
xylem-groups. x 50. 
Fig. 6. Left-hand corner of Fig. 6 more highly magnified : hk, hooked ends 
of the xylem-strand ; sc. t., sclerosed sieve-tubes; Ip , cavity-parenchyma; pa, 
parenchyma-cells among the sclerosed sieve-tubes; x. sh., xylem-sheath. At ( x) 
the sclerosed sieve-tubes are seen to be in immediate contact with the tracheides. 
x 260. 
Fig. 7. Diagrammatic transverse sections of the petiolar meristele in different 
regions of the leaf : a, about half-way up the petiole ; b, just below the insertion 
of the lowest branch ; c, about the middle of the branched portion ; d, near the 
top of the rachis ; e, in the principal vein of a leaf-segment. The protoxylem- 
groups are indicated by black dots. 
Fig. 8. Transverse section of the petiolar meristele at about the stage 7, d, 
more highly magnified : sc. t., sclerosed sieve-tubes ; P, pericycle. Note the 
disappearance of the hooks at the ends of the xylem-strand. x 180. 
Fig. 9. A scalariform tracheide after maceration in caustic potash. It becomes 
unrolled into a spiral ribbon bearing several bars of thickening in its breadth. 
X 260. 
Fig. 10. Two of the fibrous elements of the petiolar meristele (sclerosed sieve- 
tubes) in longitudinal section, x about 400. 
Fig. 11. Cells of the cavity-parenchyma: a , an older, b, a younger stage. 
X about 300. 
Fig. 12. Transverse section of a stoma. Intercellular rodlets are found in the 
substomatal cavity, x about 500. 
