292 DISEASES OF CULTIVATED PLANTS 



instances, as in species of Gymnosporangium, the two hosts 

 producing aecidiospores and teleutospores respectively, are 

 indispensable for the continuation in time of the fungus, 

 hence the removal of one host arrests the development of 

 the fungus in a given locality. 



Aecidiospores are developed in chains, uredospores and 

 teleutospores are borne singly on slender stalks. 



Heteroecism, although most pronounced in the Uredin- 

 aceae, is not entirely confined to this family. Woronin has 

 proved the occurrence of heteroecism in Sclerotinia heteroica, 

 a member of the Ascomycetes. The ascospores of this fungus 

 are produced from a sclerotium developed in the ovary of 

 Ledum palustre. The ascospores in turn infect the young 

 leaves of Vaccinium uliginosum, which produce a conidial form 

 of fruit. This conidial fruit infects the stigma of Ledum, and 

 the ascigerous form is in turn developed. 



Woronin and Nawaschin, Zeitschr. fur Pflanzenkr., 6, 

 p. 129 (1896). 



UROMYCES (LINK.) 



Spermogonia present in many species ; aecidia having the 

 peridium usually well developed; sori of uredospores flat, 

 small; sori of teleutospores more or less powdery, teleuto- 

 spores i-celled, with a single germ-pore, stipitate ; secondary 

 spores almost colourless, ovoid or elliptical. 



Colchicum smut (Uromyces colchici, Massee) proved de- 

 structive for three seasons in succession to the foliage of a 

 bed of Colchicum speciosum^ and during the third year the 

 disease spread to Colchicum bavaricum and C. autumnale that 

 were growing on either side of the diseased batch. Leaves 

 only are attacked, the lowest and oldest leaf first showing the 

 parasite, which follows the leaves upwards in the order of 

 their appearance. The sori are exceptionally large, elongated 

 on the leaf-sheath, often in circular groups on the blade of 

 the leaf. The sori remain for a long time covered by the 

 epidermis, which at length cracks and exposes the black 

 mass of spores. Teleutospores are alone known. 



Diseased leaves should not be allowed to rot on the 

 ground, but should be removed before the spores fall ; and in 

 the case of diseased plants it is advisable to remove the bulbs 

 to ground that is not infected with spores. 



