DISEASES OF GIIEENHOUSE PLANTS. 32? 



shaped cavity in which the spores are formed. This 

 constitutes what is known as the secidio stage of the rust. 

 Later in the season the pustules take on a reddish color, 

 and spores that are then present are of about the same 

 size and shape as the cecidio spores, but they are covered 

 with minute Bpi nes and are arranged singly upon ehort 

 stalks or basidia. Towards the end of summer, the red- 

 dish, spots are replaced by minute black bristle-like 

 tufts, in which the winter or teleutospores are found. 

 These are compound, being separated by cross partitions 

 into from five to ten cells, and are borne upon compara- 

 tively short stalks, which are thickened toward their 

 base. 



The secidiospores and uredospores serve for the 

 reproduction of the fuugus during the summer. If the 

 conditions are favorable, they germinate readily, but if 

 kept dry for a few weeks they lose their power. 



It is the function of the teleutospores, with their 

 thick cell-walls, to carry the fungus through the winter, 

 and in the spring they germinate, sending out thickened 

 tubes which bear at their ends small globular bodies 

 called sporidia, which are light and easily borne about 

 by the wind, and thus serve for the dissemination of the 

 fungus. If they fall upon rose leaves, they quickly 

 germinate, and soon produce new rust spots. 



If the disease appears upon a plant, the affected 

 branch should be cut off and burned. By spraying with 

 Bordeaux mixture and other copper compounds, the 

 spread of the disease can be prevented. The so-called 

 Rose Phragmidium (P. speciosum, Fries) is closely allied 

 Id the above, but differs in confining itself to the stems 

 and seldom infecting the leaves. It forms its regular 

 hlack masses of spores late in the season upon the stems. 

 ?hese spores (teleutospores) differ from those of the 

 rose rust in having long, slender stalks. The spots f le- 

 niently surround the stems, thus completely girdling 



