44 DISEASES OF CULTIVATED PLANTS 



2. Similar intumescences were produced by means of weak 

 solutions of copper chloride, copper acetate, copper nitrate, 

 and copper sulphate when sprayed in very fine drops on the 

 surface of the leaves. 



3. The intumescences were formed in larger numbers on 

 the lower surface of the leaves than on the upper surface of 

 the leaves. 



4. Intumescences were formed independent of soil or 

 atmospheric conditions, so that the heat and water supply- 

 had nothing to do with their formation. 



5. Intumescences must be regarded as a result of the 

 stimulating activity of chemical poisons, sprayed upon the 

 leaf in weak solutions. 



6. The stimulating activity exerted is due to the formation 

 of compounds within the cells of high osmotic tensions, these 

 compounds being either compounds formed by the copper 

 salts with parts of the protoplast, or compounds formed as a 

 result of a stimulus exerted, as evidenced by the presence of 

 large amounts of oxidizing enzymes as a result of indirect 

 stimulus exerted by the salts upon the leaf surface. 



In all instances the general morphology and structure of 

 these warts, independent of relative size, is the same. A 

 section through a young wart shows certain of the cells form- 

 ing the spongy parenchyma much enlarged, growing outwards, 

 and raising the epidermis, which at a later stage becomes 

 ruptured. The enlarged cells increase enormously in size 

 and grow outwards, forming a wart projecting considerably 

 above the general surface of the leaf. These giant cells are 

 very thin-walled, the outermost ones only containing air, the 

 more deeply imbedded ones containing considerably reduced 

 chlorophyll grains. At first the cells forming the spongy 

 parenchyma are only involved in the formation of the wart, 

 but at a later stage the cells of the palisade tissue also 

 begin to increase in size and become much elongated in 

 the direction of the projecting portion of the wart. Reagents 

 show that the older cells of the warts are more or less suberised 

 and liquefied, and become broken up into a scurf-like mass. 



Atkinson, G. F., 'Oedema of Tomato/ Bull. Cornell Agric. 

 Eocp. St., No. 53 (1893). 



Dale, E., ' Investigations on the Abnormal Outgrowths, or 

 Intumescences on Hibiscus vitifoliusj Phil. Tran. Roy. Soc., 

 Ser. B, 194, p. 163 (1901). 



