Where are the fine, mealy, substantial "apples of the earth" gone?--and Echo answers, "Where?" They are not to be found at the present day. The farmers have suffered great losses, in some instances by a partial, and in others by a total, failure of their crops. Numberless experiments have been tried to prevent this great national calamity, yet they have all proved abortive, for the simple reason that we have been only treating the symptoms, while the disease has taken a firmer hold, and hurried our subjects to a premature decay. Different theories have been suggested with a view of explaining the causes of the potato rot, none of which are satisfactory. We have the "fungous theory," "insect theory," "moisture theory," "theory of _degeneration_," and "the chemical theory of defective elements." In relation to the "fungous theory" we observe that fungi inhabit decaying organic bodies. They are considered to be a common pest to all kinds of plants, like parasites, living at the expense of those plants. We do not expect to find fungi in good healthy vegetables, at least while they possess a high grade of vital action. It is only when morbid deposits and chemical agencies overcome the integrity or vital affinity of the vegetable that fungous growth commences. In the fungous development, the living parts of the vegetable are not always destroyed; yet these fungi obstruct vital action by their deposits or accumulations; hence the small vessels that lead from centre to surface are partly paralyzed, and the power peculiar to all vegetables of throwing off useless or excrementitious matter is intercepted. This is not all. The process of imperceptible elimination, which might restore the balance of power in any thing like a vigorous plant, is thus impaired. Now, it is evident that the fungi are not the cause of the potato rot; they are only the mere effects, the symptoms: preceding these were other manifestations of disorder, and these manifestations, in their different grades, might with equal propriety be charged as causes of the potato rot. The deterioration of the potato has been going on in a gradual manner for a long time. A mild form of disease has existed for a number of years, making such imperceptible change that it has escaped the observation of many until late years, when the article became so unpalatable that our attention has been called to it in good earnest; and by the aid of the microscope we have discovered the fungi. Has this discovery benefited the agriculturist? Not a particle.