VENTURIA. 



219 



placed them in the genus Venturia. His investigations are, 

 however, not quite complete. 



The scab or black spot of apple and pear is a very familiar 

 disease in America and elsewhere. It attacks leaves, young 

 shoots, and fruits. Dirty greenish spots appear first, then enlarg- 

 ing, they run together, and darken in colour till almost black. If 

 the attack occur on young foliage, it may be dwarfed and killed ; 

 the newly-formed fruit will in such cases be attacked, shrivel 

 up, and fall. If the attack be deferred till the foliage and fruit 

 are well advanced, then spotting results and the fruit remains 

 hard, perhaps cracks. The conidia are oval, unicellular, and 

 yellowish-brown ; they are produced from short conidiophores 



Fig. 107. — Venturia (Fusicladium) dendriticum forming brown spots on an 

 apple ; those still in the earlier stages have a radiate margin and bear conidia. 

 The enlarged section shows two rows of large-celled parenchyma of the apple, 

 covered by a stroma of pseudoparenchyma bearing conidiophores and conidia. 

 (v. Tubeuf del.) 



with warty prominences which grow on spots of leaf or fruit 

 (Fig. 107). The perithecia (as yet described) are distinguished 

 by black bristles surrounding the pore, and occur on fallen 

 leaves. The asci contain eight greenish ovoid spores with two 

 or three cells. 



In addition to the injury to leaves and destruction of young 

 fruit, the disfiguration of the apples is a cause of considerable 

 monetary loss. Dilute Bordeaux or copper sulphate mixture 

 applied before the opening of buds, and once or twice after 



