It will be remembered by those gardeners who read the 'Horticultural Transactions ' of 1828, that the President astonished the ordinary plodders in the culture of this tuber by his superior culture of the plant, and its extraordinary productiveness under his directions. A strong kind which he obtained from the Society, called Lankman's, he cultivated, and the produce was at the rate of 539 bushels, of 82 lb. to the bushel, per acre; and from the Old Ashleaved Kidney, he obtained at the rate of 695 bushels per acre, of 82 lb. to the bushel.

"No one " would believe Mr Knight's statement. Mr Loudon wrote against ifc; but I believed it, as I had assisted to take up a crop of Potatoes in the north of England which was at the rate of 18 tons per acre. This was done long before the 'Gardeners' Magazine' started, and at a place where the great philosopher Mr Knight had never been heard of, and where the gardener's library-consisted of Abercromby, Culpepper, Down's Catalogue, and the Lichfield Translation of the Genera. Yet Mr Knight's crop of Ashleaved Kidneys of 695 bushels and 3 pecks exceeded the rate of 25 tons to the acre.

After these statements, the most astounding part of it is that these "rule of thumb " gardeners in the north of England should have obtained such a maximum of produce from the Potato before there were any scribbling gardeners to direct them. Though they may have read Newton's theory of gravitation, they in all probability never applied it to the culture of the potato in the light that Knight did; but they arrived at their maximum by dint of observation in their failures and successes.

Be that as it may, I went to Downton Castle to see the Potatoes, and Mr Knight, with fork in hand, took me to his Ashleaf and other kinds of Potatoes, and he turned out some roots, the crop being such as would have convinced any doubter that his statements in the ' Horticultural Transactions' were correct. I gave him a little of my previous experience in the culture of the Potato, which enabled me to be a stanch believer in his immense crops of the then delicate Ashleaved Kidney Potato. I had read Mr Knight's theory that plants, like animals, have but a given time allotted to them on the earth, and I asked him what age from seedlings he thought the potato began to fail. He said that at about 14 years old the generality of them reached their maximum of productiveness, aud after that they gradually failed, till at length no one would grow them, and they became extinct.

I remarked that the Ashleaf appeared to be an exception to the rule, and he said it was.

Now I never read of this gentleman's sayings in bygone days, but the couplet of Burns forces itself on my memory - "Thus by some hedge the generous steed deceased, For half-starved snarling curs a dainty feast".

That this philosopher's bones have been well picked there cannot be a doubt; but then the more we pick them, the more brilliant does their phosphorus appear.

Hence in these observations I shall not only repeat what he, viva voce, advanced towards an explanation, as it afterwards proved, of the cause of the so-called Potato disease, long before it absolutely showed itself, but I shall endeavour, however roughly, to utter what he would have advanced, as a means of preventing such a calamitous loss of Potatoes as we now so frequently suffer, had he been with us.

It is patent to vegetable physiologists that the Potato is a plant, both stem and tuber, composed chiefly of cellular tissue, its vascular tissue being but trifling even in the haulm when ripe in the autumn. That this latter tissue, or something approaching it, was produced in the haulm of late Potatoes more than half a century ago, was clear enough, as without careful handling the men got cuts on their hands when drawing the tops to make way for the plough to turn out the tubers. Such was the healthy condition of these (let us call them) vascular potatoes, that I have seen them stored 6 feet thick, and found perfectly sound in the spring.

The disease in question had never been heard of, but we did occasionally hear of the "curl" having appeared on some favourite sorts. It would now appear that the "curl" was a forerunner of the serious events which we have seen befall the Potato. The "curl" appeared on the vascular kinds more generally than on the cellular sorts; and when this disease so far emaciated the crop, the kind was abandoned; but the early or cellular kinds and second earlies, with their broad succulent foliage and almost as succulent stems, merited and obtained the attention of the gentlemen's gardeners.

The Ashleaved Kidney took the first place for a long time.

Amongst a great number of new kinds of Potatoes which "came out" for the approbation of the public, the Lapstone with its varieties appeared, and, in my humble opinion, the climax (in beauty of plant, in smooth perfection of tuber, in produce of crop, in flavour) was reached. It also affords a:'dish" of good Potatoes from July to July; in fact, no other kind is recpiired when it is free of disease. But it was deficient in that racy flavour which the Ashleaf possesses, for a short period of its season, and that is from the time the haulm takes a yellowish colour until they appear dark brown. To supply the table with this racy-flavoured Ashleaved Potato (though it is now doubtful if we have not lost it), I used to plant successional crops from January to June; and it is from that practice that I think I am able to prove Mr Knight's theory correct - that the potato never had any "disease " save that which arises from old age. A part of this garden falls sharpish to the north-east; and when the late-planted Ashleaf Potato was located there, and a cold rainy autumn set in a few days earlier than usual, the haulm turned "blotchy," a part of the tubers rotted, and the other part was used for seed, as they were not good for the table.

As we thought we knew the cause, no more was said about it at the time. However, the late-planted crops of this kind (we did not try any other sort) became so unsatisfactory that we discontinued late-planting long before the so-called disease showed itself so extensively as it did in 1S46. As the "disease" appeared in so many different kinds of Potatoes, I quite agreed with the generally-accepted opinion that atmospheric influence was the mysterious cause of the lamentable failure of the Potato crop. Observation, hearing, and reading, keeping pace with time, I was obliged to "hark back" to Mr Knight's theory - i. e., that the days allotted to each kind from seed are numbered, and all the pains which have been taken by so many first-class practical men, as well as by a phalanx of lynx-eyed philosophers, to prove to the contrary, is visionary, in fact mere dreams. The experience of the last year is proof sufficient of my own visionary ideas, when I lost from 50 to 80 per cent of the best Potato ever known to me - the Lapstone, or Haigh's Seedling.

It is hardly necessary to say any more in proof of this theory of the late President of the London Horticultural Society being the true one, of the cause of the failure of the Potato of late years, when the atmospheric conditions were such as to neutralise the efforts of those old cellular kinds to ripen their tubers, as well as other short-lived kinds. I cannot recount, however, the number of kinds which have appeared and become extinct since the disastrous year of 1816, when we had a fine spring till the 28th May, when a severe frost occurred and destroyed the products of the garden; Potatoes nearly ready for market were killed. This was followed by a wet summer and autumn, and though the Barley rotted on the ground in the north of England, yet the Ashleaf and all the other kinds of Potatoes were sound.

Thousands of people became victims to the disease brought about by empty stomachs; and had not the Potato been sound, tens of thousands would have perished by the same means.

Hence we may surmise, from what has happened, that the Potatoes have gradually declined in strength since those days, till they have fallen inactive under an atmosphere which overpowers their functions, already debilitated by age.

Had we been standi believers in Mr Knight's doctrine, we might have avoided much of the loss we have sustained.

But lured as we have been by early and highly productive, racy-flavoured, and exceedingly cellular kinds, which from their delicacy are short-lived, we neglected, through our ignorance and unbelief, the vascular and consequently more hardy kinds, which do not collapse under the same atmosphere as the above-mentioned sorts.

Our attempts in the future are now clear enough.

It is not probable that we shall abandon our favourite cellular kinds; but we must rear seedlings from the vascular kinds, and not "cross " them with the cellular sorts, as a means of furnishing us with late Potatoes that will withstand such rigorous years as those of 1816 and 1872.

Mr L. G. Moore tells us, in the Germantown 'Telegraph' of April the 9th, that he formerly had an old kind of Potato called the " "Whig," which was an excellent Potato, and which was never diseased, and it maintained its good qualities late in the following summer; but it was a poor cropper, and became supplanted by the Peach Blow. Therefore let us apply to our American cousins for the "Whig Potato, and rear seedlings from it without crossing it with any other kind, and let us see what can be done in this direction.

This theory of the most cellular varieties of the Potato suffering more than the robust kinds by excessive moisture and a low temperature is not confined to the humble Potato, as it holds good in other kinds of plants and trees - the Peach and the Apple, for instance.

The Peaches here suffered so much by the late rains that many of them "died back " considerably. A favourite Balgowan Nectarine, that I thought was a hardy fellow, had not a good blossom upon it. The Eibston Pippin Apple suffered severely, and Alfriston dropped every leaf early in the autumn, and is now to all appearance dead.

There is another of Mr Knight's theories which I have proved true in practice.

When looking over his Peach-trees, which had been seriously affected with the "blister," a cryptogam which very much damaged the foliage of the Peach, about 40 years ago, he observed that the Peach did much better, and the trees lasted longer, when budded as standards or half-standards, not only because the manipulator had a chance of performing his work better than when standing on his head, as it were, but because the sap received such a degree of elaboration in the stem of the stock as rendered it more congenial to the sap of the bud, and hence a more complete union of the two was made. In proof of which I found a half-standard, glandless, rough-leaved Royal Georre Peach here 45 years ago, which is still bearing a crop of fruit, while during that time several generations of dwarfs have been sent to the wood-pile. I presume it is imperfect workmanship which lets moisture to the crude sap, and disease is established.