15 



warm and genial — (a few frosty nights have little influence on 

 the wheat, and none upon the fungus), — and gentle warm 

 breezes prevail, the wheat plant grows rapidly and becomes 

 very rank and succulent. The spores of the fungus escaping 

 from the grass rise and are wafted upon the crop, adhering to 

 the surface of the plant, which is then generally found to be 

 slightly moist near the ground, and enter at once unseen and 

 unsuspected upon their silent course of destruction As long 

 as only the leaves of the plant {i.e., wheat and other grasses) 

 are attacked the effect upon the seeding process is compara- 

 tively insignificant ; it only becomes serious when the stalk 

 becomes affected to any considerable extent. "We have, there- 

 fore, to consider the structure of this part of the wheat plant 

 for a moment at this stage of our inquiry. 



A very thin and smooth skin forms the outermost layer, 

 immediately below which follows a layer of minute micro- 

 scopical plates formed of pure silica (the same substance that 

 forms quartz, flint, &c), acting like a coat of mail in protecting 

 the underlying delicate fibres, canals, and cells (containing 

 the life- sub stance or protoplasm of the plant) while engaged 

 in their office of nourishing and building up the body thereof. 

 The edges of these stony plates are toothed and notched, and 

 fit, in a normal state of health, closely into each other, thus 

 giving strength to the stalk without- rigidity, only leaving open 

 exceedingly small apertures called stomata, pores or breathing 

 holes, but much too small to allow any sjDores to enter. But if 

 the plant be surcharged with sap, through super-abundant 

 moisture in the ground, this, in combination with increased 

 temperature, will result in swelling out the cellular tissues 

 unduly, separating the edges of the armour plates and 

 enlarging the various openings or pores. The sj)ores of a 

 fungus alighting upon the exterior of such a plant when 

 moistened, at once begin to germinate. Their lower surface 

 extends, tube-like, and pushes a fine point into the next pore 

 or even pierces the softened cuticle, thus penetrating the inter- 

 cellular spaces between the abnormally separated silicious 

 plates. Through this delicate tube the contents of the spore 

 follow, and the new life begins by the formation of a network 

 of delicate fibres, called the mycelium, upon which in due time 

 sporangia or sporebearers are formed. Analagous to many 

 animal parasites, the fungoids do not kill or' even seriously 

 incommode their host for some time, the vital action of the 

 more important organs being left almost undisturbed. But, as 

 soon as the preliminaries for their own propagation are com- 

 pleted, all regard for their host ceases and operations are 

 carried on at an accelerated rate. 



The roots, &c, of the wheat plant have at this stage collected 



