BY D. McALPINE. 489 



aphides, cfec, to secure indirectly the protective services of the 

 ants, wherever there were birds, &c., available to keep the former 

 under control within safe limits. Therefore the reduction of the 

 birds, itc, by man, stimulated the limitless increase of the scales, 

 aphides, psyllids, aleurodids, &c., and at the same time also the 

 numbers of the ants, which helped to clean away the exudations 

 of those of their pets left by the birds, &c., were greatly diminished. 

 Hence excess of honey-dew insects and of their produce, which is 

 naturally availed of by the low fungoid germ which, under normal 

 conditions, had to be satisfied with the 'crumbs' left by the higher 

 agents " 



There is here a somewhat complex relation between the different 

 forms of life used b}' the plant for protective purposes, and if one 

 of the checks is withdrawn or diminished, the balance is disturbed 

 and disorder ensues. 



1. The Scale or other insects are used indirectly to attract the 

 ants b}' their sweet secretions. 



2. The Ants like a standing army protect the foliage against 

 the attacks of leaf-eating animals. 



3. The abundance of honey-eating BirJs is necessary to keep 

 the scale or other insects within reasonable bounds. 



4. The reduction of these birds by man tends to favour the 

 increase of the scale insects and their produce 



5. The scale and other insects now get the upper hand, and the 

 ants protecting the insects also favour their incj^ease. 



6. The consequence is superabundance of honey-dew, and this 

 is taken advantage of by the germs of the fungus to spread and 

 multiply. 



Thus the destruction of the honey-eating birds has brought 

 about an increase of the honey-dew and of the "Sooty Mould " 

 which lives upon it, so that it is not only insectivorous birds 

 which ought to be protected for the benefit of the grower. 



It is interesting to observe the appearance of other checks to 

 the spread of the scale or other insects. Here there are two 

 parasitic fungi found respectively on the red and the white oi-ange 

 scale, Microcera coccophila, Desm., and J/, rectispora, Cooke. In 



