No. XVI.] APPENDIX. 255 



3. Aphides suck the juices of plants after having pierced the cuticle. 



4. Aphides, by suckjng the sap, impair its qualities. 



5. The sap, being injured, no longer performs its proper functions. 



6. The injured sap cannot properly nourish the plant. 



7. TJnnourished or imperfect tissue is apt to die. 



8. Partial death, following the attacks of aphides, may be local at the 

 part affected, or remote ; that is to say, at a distance from the attack. 



9. The total death of the plant may arise from the death of a part 

 necessary to the whole. 



10. Wnd plants, or plants in a condition calculated to develop fibre, 

 will resist the attacks of the aphides. 



11. Highly cultivated plants, or plants not under circumstances 

 favourable to the formation of fibre, ill resist the attacks of aphides. 



12. Plants are most injured by aphides at that period of their growth 

 when they are required to deposit most fibre. 



13. Plants having their tissues damaged by aphides are more or less 

 apt to propagate diseased tissue in all their future growths. 



14. The damage to the plant hastens the transformation of aphides to 

 the perfect state. 



16. The attacks of aphides are almost invariably followed by the 

 growth of fungi." 



In 'My Garden,' published in 1872, in the chapter on Fungi, Mr. 

 Smee again puts forwards his theories on the subject of the potato disease, 

 for at page 363 we find these words : " One form of fungus has attracted 

 much attention of late years, as it has been represented to be the cause of 

 the potato disease. Prom my own observations I beKeve that an aphis 

 invariably punctures the leaf before the attack of the fungus. It is 

 possible that the punctures of the insect allow the zoospores of the fungus 

 which have ciliae to penetrate into the interior structure of the leaf, whence 

 the mycelium spreads into every part of the texture of the plant. The 

 fungus appears as a white powder to the eye, but when examined by a 

 microscope the white patch proves to be a forest of little branching stems 

 surmounted by oval bodies. It was called by Berkeley Botrytis infestans, 

 and now the genus is named Permioypora." A figure of this fungus is then 

 given. 



No. XVI. 



ELEMENTS OF ELECTRO-BIOLOGT ; ob, the Voltaic Mechanism 

 OP Man, being a Nattjeai System of Mental Phllosopht. 

 By Ar.FEED Smee. Published February 1849. (Fi-om ' Chambers's 

 Edinburgh Journal.') 



Me. Smee not only confirms the conclusions of prior investigators ; he 

 goes further, and endeavours to account for mental as well as physical 

 phenomena. " The physiological matter," he observes, " required two lines 

 of investigation : the one having reference to the ultimate structure of 

 organic beings ; the other to the actions taking place in them. . . . By the 

 electro-voltaic test, the mechanism of nervous actions has been determined. 



