564 Waterhouse . — Studies in the Physiology of Parasitism. VII. 
4. Ward, H. Marshall (1903) : On the Histology of Uredo dispersa , Erikss., and the ‘ Mycoplasma 
Hypothesis’. Phil. Trans. Roy. Soc. Lond., B, cxcvi, p. 2 9. 
5. Gibson, C. M. (1904) : Notes on Infection Experiments with Various Uredineae. New Phytol., 
iii. 184. 
6. Eriksson, J. (1911) : Der Malvenrost. 
7. Blackman, V. H. (1903) : On the Conditions of Teleutospore Germination and of Sporidia 
Formation in the Uredineae. New Phytol., ii. 10. 
EXPLANATION OF FIGURES. 
The host tissue in every case is that of the leaf of Berberis vulgaris. 
All rigures were drawn with the camera lucida under a Koristka -inch semi-apochromatic oil- 
immersion objective and No. 8 eyepiece, except Figs. 1-3, which were drawn under a Leitz ^inch 
oil-immersion objective and No. 12 eyepiece. 
Fig. 1. Sporidium germinating on slide and producing a single germ tube with a mucilaginous 
sheath. Drawn from living material stained with weak aqueous gentian violet, x 2,000. 
Fig. 2. Germinating sporidium producing two germ tubes with mucilaginous sheaths ; material 
as in Fig. 1 . x 2,000. 
Fig. 3. Germinating sporidium producing three germ tubes-: material as in Fig. 1. x 2,000. 
Fig. 4. Germinating sporidium producing a vesicle ; material as in Fig. 1. x 1,560. 
Fig. 5 Germinating sporidium producing vesicle with a mucilaginous investment; material as 
in Fig. 1. x 1,560. 
Fig. 6. Sporidium germinating and producing a vesicle which is developing a germ tube 
above; material as in Fig. 1. x 1,560. 
Fig. 7. Sporidium germinating on barberry leaf and producing a vesicle, x 1,560. 
Fig. 8. Sporidium on barberry leaf, germinating with production of a simple germ tube, the tip 
of which is adpressed to the surface of the leaf, x 1,560. 
Fig. 9. Sporidium attached to leaf and producing a beak-like protuberance at one end. x 1,560. 
Fig. 10. Beak-like projection of sporidium producing an indentation of the cuticle, x 1,560. 
Fig. 11. Outgrowth from sporidium pressing upon the cuticle and forcing up the end of the 
sporidium. x 1,560. 
Fig. 12. Sporidium producing a longer beak-like process with its densely protoplasmic tip 
closely pressed against the cuticle, x 1,560. 
Fig. 13. Sporidium producing a style-like infection hypha which has pierced the cuticle. The 
section is cut in such a way that the actual connexion between the style and the sporidium is not 
shown, x 1,560. 
Fig. 14. .Sporidium showing the infection hypha which has penetrated the whole thickness of 
the epidermal wall, x 1,560. 
Fig. 15. Infection hypha, developed from a germ tube, which has pierced the cuticle, x 1,560. 
Fig. 16. Germination of sporidium has led to the formation of irregular vesicles. An infection 
style has penetrated the epidermal cell and is beginning to swell at the tip. x 1,560. 
Fig. 17. A later stage of penetration. The vesicle in the epidermal cell has increased in size, 
x 1,560. 
Fig. 18. Larger vesicle showing three nuclei, x 1,560. 
Fig. 19. Two epidermal cells which have been invaded, showing the branching of the mycelium 
arising from the infection vesicle. The shrivelled remains of the germinated sporidia are to be seen 
on the leaf surface, x 1 ,560. 
