FUNGOID PESTS OF CULTIVATED PLANTS. 123 



The conidia, or sporules, have a very peculiar form, consisting of two 

 nearly equal uncoloured cells attached end to end, and two smaller cells 

 on opposite sides at the point of attachment, so as to present an unequal 

 cross-shaped body. These conidia are produced superficially, in consider- 

 able numbers upon the leaves, extending also to the fruit (18-20 x 12 /x). 



It also attacks the leaves of the Quince. Pear fruits when attacked 

 are liable to crack ; hence a common name for the disease is "cracker." 



Spraying with Bordeaux mixture holds the disease in check, using a 

 very dilute solution. Dead leaves should be collected and burnt. 



Sacc. Syll iii. 3504 ; Mass. PL Dis. 276, fig. 73 ; Galloway, Eep. 

 Agri. U.S.A. 1889, p. 357, pis. viii. ix. ; Tubeuf, Dis. 480. 



Pear-leaf spots, as distinct from those on Apple, are also recorded as 

 Phyllosticta pirina and Phyllosticta piricola in Southern Europe, Asco- 

 chyta piricola in Italy, and Septoria nigerrima in Germany. 



PEAR SCAB. 

 Fuxicladium pirinum (Lib.), PL X. fig. 11. 



Between the Pear scab and the Apple scab there seems to be very 

 little difference except in name. The conidia are the same in size, and 

 the little difference in form can scarce be material. 



The external manifestations, both on the leaves and the fruit, are very 

 similar : in the former case both form irregular velvety olive patches, 

 which are apt to have a dendritic appearance on Apple leaves. 



The threads are short and rather robust, and the conidia are typically 

 rather fusiform, being attenuated towards each end (28-30x7-9 /x), 

 and we have never met them with a transverse division, whereas those of 

 the Pear scab are usually of a club shape, and often divided into one large 

 cell and one small one. 



Known in Germany, Austria, Italy, Portugal, and France. 



For remedies see also Apple Scab. 



Sacc. Syll. iv. 1643 ; Mass. PL Dis. 304, fig. 81. 



A mould with fusiform conidia, not unlike Fusarium, is recorded as 

 affecting ripening Pears in France. It has been named Discocolla pirina. 



AMERICAN PEAR BLIGHT. 

 Micrococcus amylovorus (Burr.), PL XI. fig. 25. 



Pear blight, or fire blight, is known only in North America, and was 

 first observed in 1780, but no description of it until 1817. " It frequently 

 destroys trees in the fullest apparent vigour and health in a few hours, 

 turning the leaves suddenly brown, as if they had passed through a hot 

 flame, and causing a morbid matter to exude from the pores of the bark 

 of a black ferruginous appearance." The results of epidemics have been 

 most disastrous, especially the memorable year of 1844. 



Various conjectures have been made as to its cause, the last of which, 

 the bacterial, advocated by Professor Burrell, was supported by a long 

 series of experiments by inoculating healthy branches with the juices of 



