VI ANIMALS AND PLANTS 185 



framework becomes blackened, sodden, and 

 withered. 



In structure, however, the Peronospora is as 

 much a mould as the common Penicillium ; and 

 just as the Penicillium multiplies by the breaking 

 up of its hyphae into separate rounded bodies, the 

 spores ; so, in the Peronospora, certain of the 

 hypha3 grow out into the air through the interstices 

 of the superficial cells of the potato plant, and 

 develop spores. Each of these hyphse usually 

 gives off several branches. The ends of the 

 branches dilate and become closed sacs, which 

 eventually drop off as spores. The spores falling 

 on some part of the same potato plant, or carried 

 by the wind to another, may at once germinate; 

 throwing out tubular prolongations which become 

 hyphae, and burrow into the substance of the 

 plant attacked. But, more commonly, the con- 

 tents of the spore divide into six or eight separate 

 portions. The coat of the spore gives way, and 

 each portion then emerges as an independent 

 organism, which has the shape of a bean, rather 

 narrower at one end than the other, convex on one 

 side, and depressed or concave on the opposite. 

 From the depression, two long and delicate cilia 

 proceed, one shorter than the other, and directed 

 forwards. Close to the origin of these cilia, in the 

 substance of the body, is a regularly pulsating, 

 contractile vacuole. The shorter cilium vibrates 

 actively, and effects the locomotion of the organ- 



