750 



FUNGI 



More frequently, however, if the mould is allowed to remain 

 unchecked and the weather is unfavourable to the growth of 

 the hop plant, the patches, especially on the lower surface 

 of the leaves and on the young hops, become covered with 

 extremely small, dark, rusty-brown specks, and the white, dusty 

 character of the spot gradually disappears. 



The time at which mould is first observed varies with the 

 season. Gardens once seriously attacked and neglected are 

 always specially liable to an annual recurrence of the disease, 

 unless measures are taken to get rid of the trouble by methods 

 described below. 



Cause. — The disease is caused by the fungus Spharotheca 



Castagnei Lev., whose 

 white mycelium forms 

 a ^mould-s^oV on the 

 surface of the hop- 

 leaves. In the early 

 stages of development 

 the slender hyphae of 

 the mycelium spread 

 over the surface of 

 the leaf and send 

 down short haustoria 

 or • suckers ' into the 

 epidermal cells. The 

 haustoria serve to fix 

 the parasite to its 

 ■B ^ « 1- J -J- .. r.xi host, and at the same 



Fig. 254. — .(4, Mycelium and erect conidiophores of 'Hop- 

 mould' (Spharotlieca Castagnei Lev.). (Enlarged 100 time theV absOrb from 

 diameters). 



B Portion of mycelium m of same fungus with conidio- the hop-plant the 

 phore {a) from the apex of which conidia (c) have been . 



abjointed ; c^ germinating conidium ; t germ-tube. (En- nUtTimCnt nCCeSSary 

 larged about 400 diameters). 



for the growth of the 

 fungus. 



Not long after the hyphse are established on a leaf, erect 



