344 Journal of Agriculture . Victoria. [11 June, 1917. 



Under the influence of the sunlight, and through the agency of the 

 chlorophyll or green colouring matter in the leaves, this mixture of 

 crude subsances becomes assimilated. While this process is in progress, 

 the surplus water in the form of vapour and undesirable gases are given 

 out to the air. As the sap becomes elaborated it is collected up by the 

 veins on the under surface of the leaves and, transferred to the channels 

 through which it is carried downwards to build up the new structures. 



Plate 95 shows three Jonathan leaves, natui-al size, illustrating the 

 upper surface (Fig. 1), and the under surface (Fig. 2), while Fig. 3 

 shows the foot stalk with stipules, and its continuation, the midrib, also 

 the lateral ribs removed from the pulpy cell tissue of the leaf as appear- 

 ing in Fig. 4. 



Plate 96 is a highly-enlarged section of the epidermis of the under 

 surface of a Jonathan leaf showing the stomata or breathing pores 

 through which the carbonic acid is taken in from the air, and through 

 which the leaves give off their waste. 



Plate 97 is a leaf, natural size, of the Prince Alfred variety, which, 

 while fresh and green, was boiled in a strong solution of caustic soda, 

 and afterwards bleached until it was white and dry, prior to being 

 photographed. By this means the green chlorophyll, which plays such 

 an important part in sap elaboration, was removed. Compare this illus- 

 tration with the leaves in Plate 95, which contained chlorophyll when 

 they were photographed. 



Plate 98 illustrates leaf development. These leaves are of the 

 Jonathan variety and they depict Figs. 1, 2, 3, and 4, four of the last 

 stages of leaf development respectively. Fig. 1, the smallest specimen, 

 shows a leaf which has emerged from the embryonic stage, and is of 

 considerable assistance in elaborating the tree's food, while that in Fig. 4 

 is fully grown and with maximum working power. These leaves are of 

 an inferior stunted character, and they were all taken from the same 

 tree, which is growing in poor, undrained soil. ISTote how unfavorably 

 these specimens compare with those of the same variety in Plate 95. 

 The latter were taken from a tree growing in rich, well-drained soil 

 under which congenial environment the foliage, black spot having 

 received attention, is invariably healthy and vigorous. This matter will 

 receive further consideration in connexion with cultivation, manuring, 

 irrigation, and drainage later on. 



Plate 99 shows the under surface of a skeletonized leaf of the 

 Emperor Alexander variety. This leaf was subjected to acid treatment 

 by which the pulpy cell tissue was removed, while the net work of ribs 

 and veins remain intact. 



Plat© 100 is the under surface of the same skeleton. 



{To he continued.) 



— ^ip^Xd^^ 



