260 M. C. COOKE, NOTES ON PODISOMA. 



which are developed upon rosaceous trees. The first experiments 

 were directed towards Gymnosporangium juniperi, called by him 

 Podisoma juniperinum. The course of his experiments are thus 

 detailed by himself: — * 



" On the 19th of May (1866) some fresh gathered specimens of 

 the Gymnosporangium were damped with water. During the night 

 the spores commenced to germinate in great quantity, and the 

 sporoids (teleutospores) were so abundant that they formed an 

 orange coloured powder. 



" On the 20th, in the morning, I deposited, by means of tweezers, 

 a little of this powder upon the leaves of five small sorbs (Pyrus 

 aucuparia ?), and after having damped the sown parts with some 

 drops of water, I placed the plants under bell glasses, in order to 

 keep up the necessary humidity, and to keep away all foreign in- 

 fluences. 



" On the 25th I had the satisfaction of seeing upon the leaves 

 some yellow spots due to the development of the mycelium, and on 

 the 26th and 27th little pustules began to form, indicating the 

 appearance of the speraiogones. The sporoids (teleutospores) ger- 

 minated some hours after being detached, and this germination 

 consists in this — the cellular membrane upon the sides, or on the 

 top of the cellule, prolongs itself into a very slender tube, the point 

 of which perforates the cuticle of the leaves. At its commence- 

 ment it is thick, and filled with a protoplasm of a grey (sic.) colour. 

 When it developes its mycelium, which it does at the end of a few 

 days, it invades the tissue of the leaf, and, in destroying the 

 chlorophyll, produces some circular yellow spots. 



"After the spermagones had discharged all their spermatia, and 

 were dry, no change of the leaves was shown until the end of 

 June. At that time the cellular tissue began to swell in the form 

 of pads upon the inferior face of the leaves, precisely under the 

 point occupied by the spermogones upon the superior face ; and in 

 the course of July the peridia appeared. Thus all the development 

 was terminated towards the commencement of August. 



"This trial of spores has conduced to the result expected, and 



proves that the teleutospores of Podisoma [Gymnosporangiuni) 



juniperinum, when transported upon the Sorb (in nature by the 



* Oversigt over det Kongl. Danske Videnskabernes Selskabs (1866), p. 185, 

 t. 3, 4. Kesuiue du Bulletin de la Suciete Eoyale Danoise des Sciences (1&66), 

 p. 15. 



