404 THE FUNGUS PESTS OF GARDEN PLANTS 



are shown in the accompanying illustration magnified seventy-five 

 diameters. The Peronospora is shown at A, the Fusisporium to 



the same scale at B. The 

 Peronospora is like a finely 

 branched thread of spun glass. 

 It is seen at the bottom of the 

 illustration emerging from one 

 of the organs of transpiration of 

 the Potato leaf. As the thread 

 grows it rapidly branches, and 

 produces spores or seeds at 

 the end of each branch. As 

 these spores drop off one 

 by one, the branches extend 

 by joints, and produce other 

 spores, till seven or eight are 

 produced by each branch. The 

 spores in the act of falling from 

 the branches are shown in the 

 illustration. When the spores 

 fall, they commonly discharge 

 their contents in the form of 

 THE FUNGI OF THE POTATO DISEASE smaller spores, from three to 



A Peronospora infestans ninp in niimhpr *^ <;hn\vn it 



B Fusisporium Solani UmDCr, aS lO\\nat 



C, C. When the spores and 



their contained secondary spores are further magnified to four hun- 

 dred diameters, as at D, the secondary spores or zoospores are seen 

 to be furnished with two lash-like tails, with which they can rapidly 

 propel themselves through water or upon any damp surface. 



Inside the leaf, as seen at E, are other organs belonging to the 

 Potato fungus, but further enlarged to four hundred diameters at F ; 

 the larger of these two bodies is comparable with an ovule or seed, 

 and the smaller to an anther with its pollen. The smaller com- 

 monly comes in contact with the larger, in a similar way to an 

 anther coming in contact with a stigma. The fertilising contents of 

 che smaller body are poured into the larger through a small beak, as 

 illustrated at the top of F, and the result is a resting-spore or seed 

 capable of living in a resting or seed-like condition for one or more 

 years. When the resting-pore is mature, as at G, it is glossy and rich 

 brown in colour. It does not germinate when first formed, but reserves 

 its power for a fitting time during some future autumn. 



