150 CYSTOPUS, OR ^YHITE RUST. 



No doubt, we have in heteroecism the salvation of such a 

 fungus. Not only is it carried through a dangerous period, by- 

 seeking relief at the hands of a second host, but (what is far more 

 important) it obtains reinvigoration by the new protoplasm with 

 which it comes in contact. 



It is not pretended that the hypothesis embodied in the 

 foregoing, at once explains all the cases possible, or that it is not 

 open to numerous objections ; but at any rate it is a suggestion 

 which well deserves consideration. 



In writing the above paper, the following works have been consulted : — 

 "Ann. d. Sc. Nat. Bot.," 1863. " Botanische Zeitung," 1881. " Royal 

 Micro. Soc. Journ.," 18S1 — S3. " Quarterly Journal Microscopy," 1884. 

 "Grevillea," 1872, etc. " Sach's Botany," Eng. Trans., 1882. "Cooke's 

 Handbook of Fungi." " Diseases of Field and Garden Crops." — Worthington 

 G. Smith. " Berkeley's British Fungology." 



EXPLANATION OF PLATES XV. AND XVL 



Fig. 1. — Mycelium of Cystopus, with suckers. 

 2. — Chains of conidia. 

 3. — Conidia, fully ripe. 



4. — Conidiuni protruding a membrane full of zoospores. 

 5 and G. — Development and expulsion of zoospores. 

 7. — Free zoospores. 

 8. — Oogonium with oospliere. 

 9. — Antheridium. 

 10. — Remains of antheridium. 

 11.^ — Ripe oogonium with oospore. 

 12.- — Ripe oospore. 



13. — Ditto, with tube of endospore protruding. 

 14. — Endospore fully protruded and containing zoospores. 

 15. — Free zoospores. 

 1(). — Zoospore Mxed on stoma. 

 17. — Zoosp(jre germinating. 



18. — Germ within stoma, swollen and elongated. 

 10, 20, 21.— C. candidus:— 



19 — Conidia. 20 — Oospore. 21 — Fungus on Cabbage-leaf. 

 22, 23, 24.— C. cubicas:-- 



22 — Conidia. 23 — Oospore. 24 — Fungus on Goat's- 



beard leaf. 

 25, 26.— C. BUti: — 



25 — Conidia. 20 — Oospore. 

 27, 28.-0. Fortuhuoi:— 



27 — Conidia. 28. — Oospore. 

 29.— C. Spimdosus, on Leaf of Thistle, 



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