632 



and political relations. The extensive and serious re-appearance of 

 the disease in the present crop of that useful plant, has rendered the 

 affection of equal interest this season. Many and various causes 

 have been assigned for the decay of the tubers, some of a more, others 

 of a less satisfactory nature, but none of them capable of suggesting 

 a preventative, and I am not aware that any such preventative has 

 been yet brought to trial. But the disease was looked upon last year 

 as in all probability of a transitory nature, and attention was directed 

 more to the preservation of the tubers of that year, than to the pre- 

 vention of the disease for the fului*e. It was, of course, on the suppo- 

 sition that the disease was dependant on the growth of fungi, recom- 

 mended that good tubers only should be planted in the ensuing 

 spring, but beyond this, I believe nothing further was done. It has 

 been stated that minute insects have been found on the leaves, which, 

 by making numerous punctures, destroyed the vitality of those por- 

 tions so injured, and thus caused the leaves to shrivel, and afforded a 

 dead nidus for the vegetation of the Botrytis, which is very generally 

 found on the decaying portions of the leaves. This may be true in some 

 instances, but I have very carefully examined the leaves of potatoes 

 affected with the disease, without being able to find any trace of such 

 insects on the healthy or diseased portions of the leaves. If there 

 had been any insects, these had long since disappeared, and left no 

 marks that I could discover of their ravages. As to the excessively 

 minute perforations in the cuticle, discoverable only by a high power 

 of the microscope, which have been described, they might be either 

 the result of the decay, or they might exist only in the imagination 

 of the observer, or again they might be the result of want of practice 

 in microscopic examinations. If the eminent observer Mirbel, des- 

 cribed the ultimate tissues of plants as riddled with holes or slits, 

 it may be easily believed that others less practised in the use of the 

 microscope, should be led into similar errors. But in this instance 

 we require that the insect should be be found on the potato, that it 

 should be accurately described, that it should be seen while occupied 

 in its destructive vocation, and that it should be universally observa- 

 ble or observed. Until these conditions are fulfilled, we may be 

 allowed to doubt whether this is to be recorded among the causes of 

 the disease. 



The CQunexion of certain fungi with the diseased state of the 

 leaves and tubers of the plant is of much greater importance, inas- 

 much as the Botrytis is almost universally observable on the 

 leaves of the diseased plant j and statements have been made that 



