Pethybridge — On the Rotting of Potato Tubers. 565 



Figs 



18. A ripe oospore within the oogonium. The details of the base of the oogonium ; 



antheridium and hyphae are only approximately indicated. Living 

 material, x 625. 



19. The sexual organs showing a terminal antheridium and an oogonium derived 



from a terminal incept. The beaded edge of the broken top of the antheri- 

 dium is well marked. Living material, x 425. 



20. The same as fig. 19, two days later, showing an early stage in the formation 



of the spore. Living material, x 425. 



21. Conidia showing sympodial development. Drawn after treatment with I in 



KL X 625. 



22. P. infestans, showing the funnel-shaped base of the oogonium within the 



antheridium. The upper part of the funnel is obscured by the presence of 

 portions of the browned oat-agar-medium adhering to the antheridium. 

 These also adhered to some extent to the spherical part of the oogonium, 

 but did not obscure it, and have been omitted in the drawing. Living 

 material, x 365. 



23. Sexual organs of P. Phaseoli from living material in Lima Bean Agar, 



showing clearly the course followed by the developing oogonial incept. 

 X 365. 



24. Sexual organs of Coleman's P.oinnivora var. Arecae, from his plate 18, fig. 3. 



X 835. 



25. P. Synngae Kleb. Sexual organs developed within the tissues of sterile 



carrot. The base or stalk of the oogoninm is not within the antheridium. 

 Living material, x 365. 



26. P. Cactorum Schroet. Sexual organs developed in a cover-glass film of carrot 



extract gelatine. The antheridium an is partially covered by a portion of 

 the hypha bearing the oogonium. The contents of the antheridium at this 

 stage had become very reduced in amount and degenerated, and for the 

 sake of clearness are omitted from the drawing. Living material, x 865. 



27. Sexual organs of P. Fagi developing in cover-glass film of carrot extract 



gelatine, drawn just before fertilization occurs, and showing the lateral 

 penetration of the oogonium by an outgrowth from the antheridium. 

 Living material, x 865. 



SCIENT. PROC. E.D.S., VOTj. XIII., NO. XXXV. 4 P 



