xxxvi.] POTATO DISEASE, II. PASSIVE STATE. 307 



coils of a spiral vessel. In colour the oospores are of a 

 beautiful palish-brown tint, like brown sherry ; sometimes 

 they are darker. The protoplasm within is at maturity no 

 longer seen as a loose, transparent, finely granular mass ; it 

 has become compact and slightly convolute, as illustrated 

 ready under favourable conditions to burst the walls of 

 the oospore, and, by producing a germ-tube, reproduce, 

 after nearly a year's rest, the fungus of the potato disease. 

 It may be observed here how totally different this con- 

 dition of the fungus is from Pythium vexans, D.By., 

 engraved to the same scale in Fig. 132. An original 

 microscopic slide of P. vexans, D.By., is preserved in the 

 Department of Botany, British Museum, South Kensington; 



X- 4OO 



FIG. 135. 



Peronospora infestans, Mont. 



Oospores of large size on slides A and B in the British Museum. 

 Enlarged 400 diameters. 



it may there be compared with true potato oospores 

 furnished by the Rev. J. E. Vize and ourselves. Some- 

 times oospores of the potato fungus attain large dimen- 

 sions, as in Fig. 135. The right-hand example is on 

 slide A, the left-hand on slide B, in the British Museum. 

 On an examination of a large number of resting-spores 

 it will be found that the convolute mass of protoplasm 

 within, though generally in one coil, may at times be in 

 two or even three distinct portions, which on germination, 

 will produce one, two, or three germ -tubes, as shown 

 at A, B, C, Fig. 136, enlarged 400 diameters ; in other 

 instances the interior mass becomes differentiated into zoo- 



