72 DISEASES OF FIELD & GARDEN CHOPS. [CH. 



mucli more common in some fungi than in others. The 

 stops or transverse partitions represent a slight temporary 

 rest in the growth of the threads. For a brief period 

 the spawn has exhausted its powers of extension, and a 

 septum or transverse wall is formed across the thread, 

 and from this point a new and vigorous start is com- 

 monly made. 



As the fungus -spawn of straw blight apparently 

 possesses the power of piercing the walls of the cells 

 of which the straw is built up, it follows that all 

 parts of the straw are liable to be infested and 

 pierced. This piercing causes a fatal injury to the cell- 

 structure, and every farmer knows that if his plants are 

 attacked by this blight whilst the crops are still young, 

 the growth will be stopped. The walls being pierced the 

 flow of sap is arrested, and the upper part of the plant 

 perishes from want of nutriment. In the older plants 

 the stem is often observed to throw out new roots from 

 the joint above the diseased part ; and if these new roots 

 are able to reach the earth, they sometimes carry on the 

 life of the plant in place of the old roots, which are more 

 or less cut off from the stem. The new roots are never 

 quite effectual in keeping up the supply of food and life, 

 and a stem once attacked by straw blight is said to never 

 entirely recover. 



It is curious that no one has at present recorded the 

 perfect form of the fungus which must, under favourable 

 circumstances, arise from this spawn. Such a barren 

 condition in mycelia is, not uncommon ; the fact often 

 holds good with fungi that there is an enormous 

 development of mycelium but no perfect fungus. There 

 are many more or less barren mycelia well known to 

 botanists, such as the orange-coloured fungoid growths 

 known as Ozonium; Byssus, Rhizomorplia, and many 

 others. In some instances, as in the grape mildew, the 

 spawn proceeds one step farther and produces what is 

 termed an Oidium, which, like the Isaria last described, 



