12 1 TNG OLD PESTS OF CULTIVATED PLANTS. 



conidia are produced singly on the tips of these threads. They are some- 

 what fusiform or spindle-shaped, divided by a septum in the centre into 

 two cells, and are a little longer than the threads which support them 

 (24-30 x 4-5 p), wholly colourless, but rather granular within, soon fall- 

 ing away when mature. 



Spraying is generally effective in this class of parasites. 



The present species has been recognised in Italy, Switzerland, and 

 Germany, as well as in Great Britain. 



Sacc. Fung. Ital. pi. 1013 ; Sacc. Syll. iv. 970; Grevillea, xiii. 

 p. 51. 



HELLEBORE ROT-MOULD. 

 Peronospom Ficaria (Tul.), PI. VI. fig. 5. 



Many Ranunculaceous plants are liable to attack from a destructive 

 mould of a similar kind to that of the Potato disease, and amongst 

 them are the Hellebores. The foliage is attacked by the parasite, which 

 soon takes possession of the entire plant. 



The external patches of the mould are effused, and of a dirty-white 

 colour, looking like mealy -blotches to the naked eye. 



When magnified the tufts of mould are seen to consist of erect fertile 

 threads, which are from five to six times forked in the upper portion, 

 the final branches, and those immediately preceding them, being curved 

 and bent downwards, leaving obtuse angles. The conidia are borne 

 singly on the tips of the threads, and are broadly elliptical, with a slight 

 tinge of violet. 



Besting spores are produced, for the winter, upon the internal 

 mycelium, the thick external coating being of a pale yellowish-brown. 

 These resting spores are set free in the spring, by the rotting of the foster 

 plant, and active zoospores, which are formed in the interior, then escape 

 from their temporary prison and infect the young host-plants and per- 

 petuate the disease. 



This disease is widely spread in Europe, being known in Britain, 

 France, Germany, Belgium, Finland, and Italy, as well as in Bosnia and 

 Lapland, and in the United States of America. 



Being such a complete endophyte, it is almost hopeless to attempt to 

 save plants when once they are attacked ; external applications are of 

 little avail. 



Sacc. Syll. vii. 835 ; Cooke M. F., p. 235 ; Gard. Chron. July 7, 1888, 

 fig. 2 ; Mass. B. F., p. 119. 



GERMAN HELLEBORE KOT-MOULD. 



Peronospora pulveracea (Fckl.). 



This disease, which attacks the foliage of Hellebores in Germany, 

 has not yet been discovered in Britain. Externally it much resembles 

 the British species, but the microscopical characters are somewhat 

 different. 



The size of the conidia is represented as 25-30 x 18-22 p. 



Sacc. Syll. vii. 875 ; Berlese Icones, t. 52. 



