118 



PHYCOMYCETES. 



first leaflets. The disease is spread during summer by conidia, 

 or swarming cells produced from sporangia. The passage through 



winter is effected by means of 

 oospores, resulting from fertiliza- 

 tion of an ovum in the oogonium 

 by a fertilization-tube from an 

 aritheridium. The intercellular 

 mycelium is at first nonseptate, 

 later septate, and forms small 

 haustoria. Seedlings of other 

 plants, besides those already 

 mentioned, and also succulents 

 (e.g. Sempervivum and Cactiis) 

 may be attacked and killed by 

 this same fungus. 



This epidemic cannot well be 

 combated except by methods 

 applicable only in the nursery. 

 The most effective method is to 

 plant no young seedlings in 

 plots which have already been 

 diseased, but to reserve such 

 plots for older plants to which 

 the fungus is not dangerous. If 

 the disease be not very general, 

 attacked plants may be removed 

 singly and destroyed. Since 

 moist air is very favourable 

 to distribution of the disease, 

 all nettings or trellises should 

 be removed from seed-beds 

 threatened by attack. In dry 

 airy localities there is less 

 danger to seedlings than in 

 moist. 



The fungus often appears 

 in such force that seed-beds of beech or conifers are denuded 

 of every plant within a few days, and in the forest beech- 

 seedlings may, during damp weather, be completely exterminated 

 over great areas. 



FlQ. 28. — Phylophihora Oinnivora. Cotyledons 

 and primary leaves in early stage of attack ; 

 the disease forms brown spots where patches 

 of mycelium are developed, j; natural size, 

 (v. Tubeuf del.) 



