DISEASES OF FLOWERING PLANTS 207 



ing functionless. In the development, two nuclei have been 

 found to copulate in the basidial cells. The nuclei then divide 

 and produce two or four new nuclei. A nucleus then passes 

 through the sterigmata into the developing basidiospore. The 

 most important disease-forming agent in Basidiomycetes is the 

 wet rot of carnations. 



202. Wet stem-rot of carnations. Classification: Basidio- 

 mycetes, Hypochnecc; Rhizoctonia (species) (Corticium vagum, 

 var. Solani). The wet stem-rot of carnations is one of the most 

 troublesome diseases with which the grower deals. The fungus 

 usually attacks the stem of the plant near the ground, and car- 

 nation plants which are so placed that they branch a little above 

 the ground are less liable to attacks. A branch of a plant will 

 rot off, and others soon follow. Affected plants first assume a 

 light, yellow color, the foliage of a branch wilts and later the 

 plant dies. 



203. Microscopical nature and reproduction. The myce- 

 lium lives on the roots of many plants, especially weeds, and it 

 has been demonstrated that the same fungus may attack a wide 

 range of species. This same mycelium may run over the surface 

 of the leaves. The whole finally forms thread-like strands of 

 vegetative mycelium. As these mycelial strands are torn apart, 

 they have the power of reproducing new, vegetative tissue and 

 the fungus rapidly spreads in this way. Resting structures are 

 formed as black, tuber-like bodies on the cortical tissue of the 

 stem. These serve to carry the pathogen over from one year to 

 the next. No asexual spores are formed. Basidiospores are 

 often produced on a white, webby mycelium on the stems of 

 plants just above the surface of the soil. 



204. Ecology of the disease. Injury to the stern near the 

 ground, which may result from heavy winds sweeping over the 

 fields, may cause carnation plants to be affected with stem-rot. 

 If branches split partially, near the ground, the fungus may gain 

 entrance to the tissue. 



205. Preventives. To prevent stem-rot, encourage the 

 branching of the stem a little above the ground. Do not set the 

 rooted cutting deeply in the soil. Place the plant in the soil 

 no more deeply out of doors than it was in the pot. Special 

 care should be taken in bringing the plant into the house in 

 the fall. This is naturally a great check to the growth of the 

 plant, which is materially weakened thereby. If the plant is 

 set deeply in the soil and watered too generously, stem-rot is 

 very likely to occur. 



206. Remedies. As soon as the disease is discovered in the 



