

5) 



ON THE PERONOSPORiE. 213 



PLATE XXIII. — Pekonospora nivea (UmbelUferarum) . 



Fig. 1. — Ripe conidia. 



2 and 3. — Formation of zoospores. 



2 — a. Protoplasm divided, conidia swollen, terminal papilla not 

 seen ; h. — Protoplasm withdrawn from wall of cell. 



3 — a. Sporangium enclosing fully developed zoospores ; h. — Expul- 

 sion of zoospores. 



,, 4. — Zoospores free and active. 



,, 5. — Germinating zoospores. 



,, 6 — 11. — Fragment of epidermis of under surface of leaf of 

 CEgopodium podagrasia, showing germination of zoospores, 

 and penetration of the germs in the stomata. Figs. 6 — 9. — 

 Six hours after sowing the spores. Figs. 10 and 11. — 

 Twenty-four hours after sowing the spores. 



,, 6. — Zoospore fixed on a stomata. 



,, 7. — Zoospore, with germ entering stomata. 



,, 8. — Globular swelling of the germ inside the stomata. 



,, 9. — Membrane of spore outside the stoma is empty, and only 

 attached by a very small filament to the germ, which is drawn 

 out in a tube towards a cellule of the epidermis. 



,, 10. — Germs which have entered by the stomata, thrusting their 

 extremities into the epidermic cellules, and there developing 

 suckers. 



11. — A germ like the two preceding, showing the empty mem- 

 brane of the spore outside the stomata. 



12 and 13. — Slices of epidermis of lower surface of leaf, showing 

 cut stomata by which germs of parasite have entered. Fig. 

 12 corresponds to Fig. 9, Fig. 13 to Figs. 10 and 11. 



14. — Fragment of thin slice of leaf of CEgopodium, with a tube 

 of mycelium emitting suckers into the cellules of the 

 epidermis. 



15. — Tube of isolated mycelium carrying two oogonia. One is the 

 sessile attached to &, and nearly ripe ; a is the antheridium ; 

 the other is perfectly ripe. 



)5 



jj 



jj 



PLATE XXIV. — Peronospora alsinearum. 



Development of oogonia and antheridia, x 400. a., antheridium ; 



0. , oogonium ; m. , mycelium. 

 Fig. 1. — Mycelium bearing young oogonium. 

 ,, 2. — Formation of antheridium. 



,, 3. — Oogonium separated by a partition from the mycelium tube. 

 ,, 4. — Fully developed antheridium. 



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