Letters on the Diseases of Plants. 



31 



the season, and results must not be expected to be completely satisfactory 

 the first season. This is owing to the deep-seatedness of the fungus causing 



Pig. 36.— Conidia from 

 "Black Spot" asitoccurs 

 ou the riud of the lemon. 

 Compare with Fig. 35. 



Fig. 37.—" Black Spots" on 

 the surface of an orange, 

 natural size. T hat on the 

 left is from the amalga- 

 mation of several simple 

 round si^ots. 



Fig. 35.— Conidia of the fungus causing 

 Black Spot. These ellipsoidal, colour- 

 less, one-celled conidia, measiu-ing 

 7 - 8 X 10 - 15 M, are enclosed by a 

 smooth and thin cell-wall, and are 

 borne in large numbers in tandem 

 fashion from the mycelium at the 

 base of the interior of the pycnid- 

 ium in a manner entirely similar to 

 those of the Bitter Rot of apple. 

 Comi^are with Fig. 36. 



the disease. It will readily be seen that if a disease-producing fungus is 

 growing under the surface of the skin no spray except such as would destroy 

 the skin of the fruit can reach the source of the disease. If, however, a 

 weak Bordeaux mix- 

 ture be persistently 

 applied, all the spores 

 that arise from the 

 fungus will be killed 

 as fast as they come to 

 the surface, and this 

 must in time stay the 

 spread of the disease. 

 The strength of the 

 mixture should be 

 the same as for 

 Melanose. Begin as 

 soon as the fruit sets, 

 and spray regularly 

 once in about ten 

 days for the entire 

 season. Of course 

 this need not be 

 kept up indefinitely. 

 There is an idea 

 somewhat prevalent 

 that spraying to be 

 eifective must be 

 continued in'de fi- 

 nitely, and this idea 

 sometimes causes 

 spraying to be looked upon as a losing game, and it is indeed true that 

 in many cases, at present prices, spraying, if it must be kept up in- 

 definitely, would never pay. The fact is. however, that if conscientiously 

 carried^out for an entire season, or at the outside two entire seasons, spray- 

 ing, iu the great majority of diseased orchards, would effect such a change 

 for the better that for some time, or even indefinitely, the treatments might 

 be discontinued, or at least made few iu number. Those who have looked 

 askance at spraying may, when they consider it in this light, see fit to 



-Orange attacked by both Black Spot and Melanose (?). 

 a a, Black Siiot; b h, Melanose (?). 



