Variegation 



Brief reference must be made to one or two 

 diseases which are to be regarded at present, possibly 

 because Uttle is actually known about them, as 

 constitutional, imavoidable (unless by rejection of 

 the plants likely to exhibit them), and incurable. 



Variegation is to be regarded as a disease, for 

 it is due to absence of green colour from parts of 

 foliage and stems, and this results in a check to 

 food-making and a lessened vigour of growth, but 

 it is often regarded as desirable, and is preserved. 

 It is a transmissible disease also at times, for if, e.g., 

 the variegated greenhouse Abutilon be grafted on 

 a green seedling, shoots from below the graft will 

 often be variegated. 



The mottling of leaves (without the complete 

 suppression of green colour in the Ughter portions) 

 forming the characteristic symptom of the " mosaic " 

 disease as it is caUed, seen in tobacco, tomatoes, 

 beans, sometimes in Pelargoniums, and probably also 

 in figs, is similarly transmissible and, though possibly 

 of bacterial origin, seems possibly constitutional and 

 more or less independent of cultural conditions. It, 

 too, reduces the food-making efficiency of the f oUage. 



The leaf -curl disease of potatoes is sometimes 

 apparently constitutional. Six diseases of potato 

 are characterised by leaf -curl or leaf-roU, and of 

 these two have not been traced to parasitic origin. 

 One called " curly dwarf " is characterised by 

 shortened internodes, brittle stems, small curled 



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