10 March, 1919.] A ppie ( 'nit are in Victuiia. 151 



attained full size. The cvacking and contortion, so pronounced in this 

 Bpecimen, are due to the force of contraction in the diseased part operat- 

 ing against the force of expansion in the healthy portion. This condi- 

 tion at the stage mentioned is termed " mid-season attack." Even at 

 the end of the ripening period, when fully matured on the trees, or later 

 when stored in the ordinary manner, the fruit is liable to he infected. 

 The ripe London Pippin apple, illustrated in Fig. 3, depicts this condi- 

 tion, which is called " late spotting." 



The illustrations in Plate 189 show the condition of leaves carrying 

 the spring and winter forms of spores respectively. Fig. 1 is a Rome 

 Beauty leaf suffering from early infection, and showing dense clusters 

 of black spores on its upper surface. Fig. 2 is an old Jonathan leaf 

 taken from the soil in winter. In this stage it contains the perithecia 

 which protect the asci, in each of which eiglit ascospores mature later. 

 On the return of spring, the ripe spores beeome liberated, and many, 

 finding a lodgment on the young moist leaves or fruit, germinate by 

 sending out spore-tubes which penetrate the hosts, probably entering 

 through the stomata or breathing pores in the epidermis. Having passed 

 through the cuticle, the spore-tube develops into a mycelium or root 

 system, which destroys the cells immediately beneath the epidermis 

 through which the spore-bearers soon emerge, and fusicladium spores are 

 liberated on the surface. When the mycelium in a diseased spot has 

 extended by radiation to its maximum, this part bulges upward some- 

 what from the plane of the leaf's surface. As the spots multiply and 

 extend, the leaf dries out, and puckering continues until the parasite, 

 having exhausted the nutriment of its host, is unable in this stage to 

 further vegetate and fructify. Then the leaf, having lost its vitality, 

 falls, and the mycelium changes to the stage capable of reproducing 

 the ascospores. 



The illustrations appearing in Plate 190* are highly-magnified 

 sections of a diseased apple and leaf, shown natural size in Plate 188 and 

 Fig. 1 of Plate 189, as well as the spores, &c. 



The highly-enlarged section of the perithecium in Plate 191, Fig. 1. 

 and the more highly-magnified asci. Figs. 2 and 3, containing the asco- 

 spores, were taken in early spring from a leaf in the condition of that 

 appearing in Plate 189, Fig. 2. Fig. 4 shows two germinating asco- 

 spores. 



When the early-produced leaves of the varieties more liable to early 

 infection and sensitive to attack, such as Yates and Jonathan, become 

 badly affected, they fall prematurely. The leaves subsequently produced, 

 even when apparently free from this disease, are usually of a stunted 

 character. The five Jonathan leaves in Plate 192 illustrate this condi- 

 tion. They were taken from the point of a lateral after those lower 

 down were destroyed by black spot. They are natural size, and depict, 

 in the various stages of development, leaves which would have grown at 

 least twice as large had not the earlier foliage been destroyed compara- 

 tively early in the growing season. It is evident that trees allowed to 

 become partially defoliated in this manner cannot thrive, owing partly 

 to insufficient healthy leafage to carry on the necessary sap elaboration, 

 &c., and partly to the dry, warm conditions set up in the soil around 



• Reproduced from a plate in Mr. T>. McAlpine's report on BLack Spot, and Spraying, Blilletin No. 17 

 nepartment of Agriculture (Victoria). 



