W. Robinson 137 



DESCRIPTION OF PLATES. 



PLATE XXV. 



Two almost mature aster plants from the same bed — the one diseased and the other 

 health}- — drawn from a photograph to scale. 



PLATE XXVI. 

 rTig. 1. Cortical cells of the hypocotyl of seedling aster in L.8. showing hyplia of Phyto- 



phthora growing through three cells. The hypha enters and grows through the 



protoplasm into the vacuole, x 180. 

 Fig. 2. Intracellular hypha passing through two parallel walls of a cell showing con 



strictions. x 1440. 

 Fig. 3. Similar hypha to that in Fig. 2 with tip of branch partially through a pit in 



the wall of a host cell, x 1440. 

 Fig. 4. Hyphae entering and growing through the parenchymatous cells of a medu'lary 



ray. x 180. 

 Fig. 5. Hypha entering one of the large vessels of the xylem seen in T.S. x 700. 

 Fig. 0. An intercellular hypha showing nuclei, vacuolated protoplasm and deeply 



staining granules at the junctions of the meshes of the cytoplasmic network, x 2000. 

 Fig. 7. L.8. of the outer portion of the stem of a diseased aster showing swollen hyphae 



separating the cuticle (c) from the epidermis, prior to the formation of sporangia 



on the exterior. One of the hyphae has penetrated the cuticle by a fine pore, x 180. 

 Fig. 8. One of the swollen hyphae similar to those in Fig. 7 showing several large nuclei 



and the deeply staining granules as in Fig. 6. c. = cuticle. x2000. 

 Fig. 9. A later stage of a similar hypha to that in the previous figure showing branching 



as it leaves the cuticle, x 1440. 

 Fig. 10, a, b and c. Various stages in the formation of the sporangium, x 700. 

 Fig. 11. Sporangiophore bearing three sporangia in different stages showing sympodial 



development, x 570. 

 Fig. 12. Almost mature sporangium showing large central vacuole. x570. 

 Fig. 13. Mature sporangium in which division into zoospores is beginning, x 700. 

 Fig. 14. The same sporangium as Fig. 13 ten minutes later, x 700. 

 Fig. 15. Same sporangium as in Figs. 13 and 14 drawn 15 minutes later. The zoospores 



have contracted somewhat from the wall and are more rounded. x700. 

 Fig. 16. Sporangium in which some of the zoospores have failed to be discharged — 



one is seen germinating in situ. x 570. 

 Fig. 17. Sporangium germinating conidially by putting out a hypha. x570. 

 Fig. 18. Zoospore as seen in motion showing unequal cilia and two vacuoles, x 700. 

 Fig. 19. Zoospore at rest stained to show nucleus cytoplasm and protoplasmic granules. 



x 2000. 

 Fig. 20. Germinating zoospore, x 700. 

 Fig. 21. Proliferating sporangium showing the stalk growing into the empty sporangium 



to form a second. x 570. 

 Fig. 22. Similar proliferating sporangium. There are seen the empty walls of two 



older sporangia which have discharged their zoospores. x570. 

 Fig. 23. Portion of a hypha of Fusarium. x 700. 

 Fig. 24. Mycelium of Fusarium bearing conidia. x 700. 



Figs. 10 to 18 and 20 to 24 on Plate XXVI were drawn from material in the living 

 unstained condition. 



