

212 ON THE PERONOSPOR^. 



PLATE XXI. — Peronospora infestans (x 390). 

 Fig. l.-^Oonidia-zoosporangia sown in water. Protoplasm divided, 

 2. — Zoospore, free and active. 



3. — Zoospores at rest and commencing to germinate. 

 4. — Zoospores, with long germs. 



5. — Epidermis from a stem of Solanum tuberosum^ in which three 

 zoospores of the parasite have thrust out germs whilst 

 perforating the walls. The parts of the germs outside the 

 epidermis are empty, the penetrating extremity having 

 received all the protoplasm. About eighteen hours after 

 sowing the spores. 



6 and 7. — Fragments of horizontal cuttings of the epidermis and 

 cortical tissue of S. tuberosum. The germs have penetrated 

 the epidermic cellules ; they are branched, and that which is 

 represented in Fig. 7 is beginning to perforate the interior 

 wall of the cellule which encloses it. About seventeen hours 

 after sowing the spores. 



8. — Vertical cutting of the same stem which has supplied Figs. 6 

 and 7, made twenty-four hours later, showing progress of the 

 germ through a large cellule into the lengthened cellules of 

 the cortical collenchyma (c.c). 



9 and 10. — Vertical cuttings of leaf of ;S'. tuberosum, five days 

 after sowing the spores, e.s., Epidermis of upper surface. 

 ex., Epidermis of lower surface. The filaments of the 

 mycelium grow between the cellules of the parenchyma, 

 which still appear healthy. In Fig. 10 a conidiophore is 

 emitted from a stomata (5). 



J) 



PLATE XXII. 



Figs. 1 — 4, Peronospora parasitica (x 390). 



Fig. 1. — Fragment of vertical section of pith of Capsella Bursa- 

 pastoris. A tube of intercellular mycelium thrusts a large 

 dichotomous sucker into one of the cellules. The mycelium 

 carries an oogonium nearly ripe. 



2 and 3. — Advanced stages of ripened oogonium, a., antheridium. 



4. — Germinating conidium. 



5) 

 5) 





Figs. 5—8, Peronospora ganglioniformis. 



5. — Pipe conidia. 



6.— Germinating conidia. 



7 and 8. — Epidermis from leaf of Lactuca sativa, conidia of par- 

 asite having been sown in it three days previously. The 

 membranes of the conidia are empty, and folded above the 

 epidermis ; the germs swollen with protoplasm penetrating 

 the cellules. 



