The Problems of Ecology. 19 r 
Fig. 9. Germ-tube of uredospore of Puccinia sp. from Carduss forming 
swelling in stoma of C. palustris (2nd day). 
Fig. 10. Similar to Fig. 9 (2nd day). 
Fig. 11. Germ-tube of aecidiospore of P. Rosae having formed a swelling in 
stoma of R. Ficaria has put forth two hyphae (3rd day). 
Fig. 12. Stoma of C. palustris in which germ-tube of uredospore of P. Poarum 
has formed a swelling from which it has put forth a curious hypha 
(3rd day), 
Fig. 13. Somewhat similar to Fig. 12, stoma being that of R. Ficaria and 
infecting fungus being U . Chrysanthemi (4th day). 
Fig. 14. Stoma of C. palustris shewing germ-tube of uredospore of P. 
glumarum growing straight through without forming any swelling (2nd day). 
Fig. 15. Germ-tube of uredospore of U. Chrysanthemi growing straight 
through stoma of R. Ficaria and forming swelling deep in the leaf (4th day). 
Fig. 16. Somewhat similar to last, but swelling at a less depth and is already 
dead (4th day). 
Fig. 17. Stoma of Tropceolum with germ-tube of P. Taraxaci growing through 
it, internal hypha much swollen (2nd day). 
Fig. 18. Shews a similar hypha of U. Chrysanthemi which has penetrated the 
leaf of R. Ficaria to some depth (4th day). 
Fig. 19. Germ-tube of Puccinia sp. from Carduss which has formed a some¬ 
what deep-seated swelling in the mesophyll of C. palustris and has then 
emitted a hypha from it (2nd day). 
Fig. 20. Germ-tube of U. Geranii entering C. palustris ; the part outside is still 
alive, that within the leaf is dead (4th day). 
Figs. 21 and 22 shew the different stage of development arrived at by two 
germ-tubes of P. Ccntaureae entering Valeriana (2nd day). 
Fig. 23. Germ-tube of uredospore of P. Mcnthae entering stoma of Valeriana 
(2nd day). 
Fig. 24. Germ-term of uredospore of P. pulverulenta entering stoma of 
Valeriana (3rd day). 
Fig. 25. Germ-tube of uredospore of P. g raminis entering stoma of C. 
palustris (2nd day). 
Fig. 26. Germ-tube of uredospore of C. Sonchi entering stoma of Valeriana 
(2nd day). 
Fig. 27. Germ-tube of aecidiospore of P. Poarum growing through stoma of 
C. palustris and forming swelling against a cell (3rd day). 
THE PROBLEMS OF ECOLOGY, 
By A. G. Tansley. 1 
E COLOGY may now be considered almost a fashionable study, 
but there are not wanting botanists who tacitly distrust, 
even if they do not openly contemn, a good deal of the work 
which is done under its name. This hostile attitude is not always 
wholly to be wondered at, for the subject has its own difficulties and 
dangers, and these are sometimes rather distressingly patent in 
, The substance of this essay was delivered as an Address to 
Section K of the British Association at the Cambridge 
meeting. It served as an introduction to the more special 
papers on British Ecology which occupied the rest of the 
sitting. 
