304 DISEASES OF FIELD & GARDEN CROPS. [CH. 



plasm from the oogonium now pours into the bladder and 

 becomes quickly differentiated into six or eight little 

 zoospores ; the bladder then dissolves, the zoospores swim 

 away, and the short-life cycle of the Pythium is completed. 



The phenomenon of speedy germination is foreign to 

 Artotrogus and the oogonia of Peronospora infestans, Mont. 

 The latter bodies do not remain transparent or germinate 

 at once ; on the contrary, they hibernate for at least ten 

 months, and during this long period of rest they increase 

 in size, become warted or echinulate, and attain a rich 

 palish-brown colour. 



We will now leave the potato fungus as seen in a 



X 400 



FIG. 132. 

 Pythium vexans, D.By. Enlarged 400 diameters. 



living potato leaf and take a fragment of a dead leaf, one 

 that has been destroyed by the Peronospora, such as may 

 be seen in fields and gardens in September, or, if preserved 

 with care, such as may be kept on a garden-bed till the 

 following June. A fragment of such a potato leaf is 

 illustrated in Fig. 133, enlarged, like Fig. 127, to 100 

 diameters. The upper surface of the leaf is shown at A, 

 the lower surface with two stomata at BB, and a small 

 hair belonging to the leaf is seen at C. Nearly all the 

 mycelium of the potato fungus has vanished ; a fragment 



