No. XV.B.] APPENDIX. 235 



Lancets of the gad-fly, showing the difference between them and the 

 delicate piercers of the aphis. 



Lancets of the tobanis, which are large and coarse. 

 Lancets of the blow-fly. 



Leaf of the potato, with numerous aphides incarcerated in balsam, 

 whilst in the act of feeding. 

 Leaf of diseased potato. 



Section of a healthy potato-tube with its minute cells filled with 

 starch. 



Section of a diseased tuber, with marks of the injury of the dis- 

 ease, &c. 



Another piece of diseased potato with brown and black spots. 

 Little quantities of starch after all other parts have been eaten 

 up. 



Section of a stem of wild potato with granules of starch seen 

 in it. 



A stem of potato with a beautiful specimen of a black fungi. 

 Blood-red fungus. 



Another fungus with round heads like peas, which are covered by 

 sporules. 



Celery-leaf with fungi. 

 Couch-grass with aphis and eggs. 

 Horseradish-leaf. 



Acarus farnce, which run about putrefying potatoes, destroying 

 offensive matter. One may compare this creature to a rhinoceros trotting 

 about in the jungles. 



Living aphides in a very active state. 



As yet the future prospects of the disease are doubtful, and I have 

 shown the destructive appetency of aphides. It is evident that the ba- 

 lance of nature is disturbed, and that these insects are preternaturally and 

 immensely in excess. The human species has frequently been threatened 

 with total destruction by these plagues ; but, though ten thousands of 

 mankind may have perished, we find by experience that the insects have 

 ceased and men lived. No doubt this calamity will eventually pass away, 

 though, indeed, it may not yet have reached its maximum. Up to the 

 present time we have only known the disease as increasing. It has been 

 worse last year than it was the year before ; but the ensuing season, we 

 may hope, will be healthy. No doubt many growers of potatoes will be 

 deterred from planting; but I should say, do not give up cultivating, 

 but cultivate in all cases, under the most favourable circumstances. I 

 believe few have yet been planted this year ; therefore, at all events, the 

 crop will be scarce. Yet it is not too late to plant, though those potatoes 

 which are placed earliest in the ground will have the best chance of suc- 

 ceeding, because they have an opportunity to deposit more fibre before the 

 time that the aphides appear to commence their attacks. The cost of potato 

 sets per acre last year, from the scarcity of good ones, is reported to have 

 been about eighteen or twenty pounds, which becomes a serious outlay to 

 small farmers, and will, therefore, greatly hinder their plans. If the insects 

 do appear this season, from experiments that I have tried in my own house, 



