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the plant may be likened to the roots of the wheat 

 running within the soil ; the roots fix the plant and 

 absorb the necessary food. Then the fine stems or 

 threads of the fungus which appear outside may be 

 compared with the stems of the wheat, and the seed 

 cases of the fungus, containing the little seeds, may be 

 compared with the ears of the wheat containing the 

 kernels or seeds of wheat. In the same way that the 

 wheat takes the plant food from the soil, so the fungus 

 absorbs the juices of the potato plant; but it does 

 more it sets up decay. 



The Growth of the Disease within the Plant 



The manner in which the mycelium pervades the 

 leaf is shown in Fig. 15. The small section of leaf, 

 highly magnified, is shown with lower side upper- 

 most. The aerial hyphse most commonly find their 

 way out of the leaf on the under side, as this is 

 supplied with almost innumerable small openings, or 

 breathing pores, called stomata, which admit air, from 

 which carbonic acid is extracted, to assist in building 

 up the plant. These openings afford easy egress to 

 the hyphre, particularly as the threads of mycelium 

 are able to form more readily near to the under side, 

 as the upper section is largely occupied by structural 

 cells, which, from their resemblance to palings, are 

 called palisade cells. The intermediate cells in which 

 the mycelium is most plentifully found are the living 

 cells that is, the cells are those which are actively 

 engaged in assimilating the food taken into the plant 



