ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 421 



gonal, winged internodes of the potato plant; several such 

 preparations were then laid with the sowings upwards, on 

 damp blotting paper, in soup-plates covered with bell-jars, 

 and the air kept damp. After twelve hours or longer, sections 

 were cut longitudinally vertical to the flat places on which the 

 sowings were made, and the section examined. It was not 

 difficult to obtain evidence of the germination of the zoospores, 

 and entry of the germinal hyphae, but it was only after many 

 weeks that I succeeded in preparing the really satisfactory case 

 here drawn. The razor had passed close to but not through 

 the germinal tube; the empty zoospore and first part of its 

 germinal hypha are seen lying close on the exterior of the 

 cell wall — the zoospore had come to rest in a slight depression 

 at the junction of two cells — the very fine hole through which 

 the germinal tube passed was clearly visible on focussing. On 

 reaching the anterior of the cell the hypha thickened con- 

 siderably, and passed along the roof of the cell, and was just 

 about to turn and run down the vertical wall (or possibly to 

 bore through it) where the section was made. The sub-epi- 

 dermal cells frequently contain a crimson-coloured sap, but 

 none of the cells in the preparation were so coloured. 



Figs. 7 and 8. — When the conidia of Phy tophthora infes- 

 tans are sown in water on glass slips, they frequently assume 

 the appearances figured at figs. 4, g, h, and i, after a few hours, 

 and then cease to develope further in the direction of producing 

 zoospores. Instead of doing that, the cloudy, vacuolated condi- 

 tion of the protoplasm which usually heralds the development of 

 the zoospores (fig. 4, i) is again replaced by the more uniformly 

 hvaline appearance of the earlier stage (fig. 4, h), and the papilla 

 either commences to grow out as a hypha, or a protuberance from 

 it (fig. 7) does so ; occasionally, but rarely, this hypha branches, 

 as in fig. 8. This germinal hypha, the development of which 

 stamps the conidium as an ordinary spore (in contrast to its 

 behaviour in other cases as a zoosporangium) elongates consi- 

 derably, and in some specimens attains a length equal to ten 

 times that of the conidium ; its apex then dilates into an ovoid 

 body much like the conidium from which it originated (fig. 7). 



VOL. XXVII, PART 3. NEW SER. G G 



