DISEASES OF FLOWERING PLANTS 205 



brown structures with ovoid asci containing eight brownish, 

 lemon-shaped spores. 



" A white coating of the hyaline conidia is first formed, then a 

 brown coating of the dark conidia, and finally perithecia." 



188. Ecology of disease. The causes of violet stem-rot are 

 a weakening of parent plants through improper cultural con- 

 ditions, and their constant propagation by division. This propa- 

 gation takes place after a season of flowering when the parent is 

 materially weakened by the forcing process. 



189. Preventives. Always examine carefully all plants 

 before propagating, making certain that the disease is not pres- 

 ent. Use clean sand for all cuttings, as this fungus, and several 

 others closely related, may live in a saprophytic manner on decay- 

 ing vegetable matter. Keep the temperature of the violet house 

 low, and stimulate strong, healthy tissue. 



190. Remedies. There are no remedies. Plants should be 

 carefully examined before being planted in the houses, and if 

 the disease is present, they should be discarded at once. 



191. Uredineae (Rust fungi). The principal fungi attacking 

 greenhouse plants in the Uredineae, are carnation rust and 

 rose rust. 



192. Carnation rust. Classification: Uredineae. Uromyces 

 caryophyllinus Schrank. The first announcement of the Euro- 

 pean importation of this pathogen was made by J. C. Arthur in the 

 Botanical Gazette, November, 1891. For several years it caused 

 great apprehension among carnation-growers because of its 

 rapid spread throughout American carnation ranges. Many 

 remedial measures were tried without success. The rust attacks 

 carnations in all stages of growth. The disease is first revealed 

 by light green spots on the epidermis. These quickly assume a 

 dark, red-brown color. In due time the epidermis ruptures 

 and the spores escape in masses of a rust color, giving the disease 

 its common name. 



Within recent years, improved cultural conditions and the 

 introduction, through breeding, of rust-resistant varieties, have 

 resulted in an appreciable decrease in the amount of rust present 

 in carnation houses. 



193. Microscopical nature and reproduction. The myce- 

 lium extends through the intercellular spaces of the leaves, and 

 forms patches of spore-bearing areas beneath the epidermis. 

 The epidermis ruptures, and uredospores are first produced. 

 These usually germinate at once, forming new, infecting myce- 

 lia. Later, teleutospores are produced, and constitute the 

 resting stage of the pathogen. 



