1896] A RUST AND LEAF CASTING OF PINE LEAVES 453 
EXPLANATION OF PLATES XXII AND XXIII. 
Fic. 1. Cross-section of leaf of Pinus Virginiana, showing cortical, meso- 
phyll, and fibrovascular regions. 
Fic. 2. Cortical region and stoma; ¢f, epidermis; s¢, stereomatic thin- 
walled cells; s¢’, stereomatic thick-walled cells. 
Fic. 3. Mesophyll cell and portion of endodermis, end. 
Fig. 4. Longitudinal section of portion of leaf; fd, fundamental tissue ; 
end, endodermis ; zs, mesophyll cells. 
Fig. 5. Resin duct. 
Fic. 6. Longitudinal section of leaf; ms, mesophyll; emd, endodermis ; 
fd, fundamental tissue; ss, sieve tubes; ca, cambium; sc, scalariform vessels. 
Fic. 7. Cross-section of a portion of leaf; end, endodermis; /d, fun- 
damental tissue; ¢v, tracheids; 4d, hadrome with scalariform vessels; lp. 
leptome. 
Fig. 8. Branch of Pinus Virginiana showing Coleosporium on one year 
old leaves. 
.9. Pair of leaves from the branch shown in fg. 8. 
. 10. Cross-section of pine leaf showing development of hyphe. 
. 11. Portion of sorus of fungus showing sporophores and mycelium 
. 12. Various stages in the development of sporophores. 
- 13. Beginning of the formation of two spores. 
14. Mature spores and spores in various stages of germination. 
- 15. Development of sporidia, a to g. 
- 16. Sporidium forming a secondary sporidium. 
17. Section through a sorus showing mature spores. 
18. Mycelium turned aside by the endodermis, which it never pene- 
FIG. 19. Two pairs of young pine leaves, a too old for infection, 4 the 
__ Proper age for infection (both natural size). 
