And it is equally vain to expect, as many have done, that the vigor of the plant can be restored by one generation of seedlings. The progeny of unhealthy and degenerate parents cannot reasonably be expected to be perfectly healthy and hardy. The result of upwards of a century of mismanagement, cannot be entirely obliterated by the first step in the right direction.

The fact that pear seedlings are attacked by their parasite, may seem to many a serious objection to the conclusion I am induced to arrive at; but as plants annually raised from seeds are not exempt, I do not see why young plants of the pear should offer greater resistance, when exposed to influences which affect their health. I think it may also be questioned whether a plant whose average duration is supposed to be about 400 years, is not more susceptible of injury, or more easily affected by adverse atmospheric influences in the first few years of its existence, than when in the prime of its life. This seems to be the case with the Osage orange, at least. - but possibly this can hardly be considered a case in point, inasmuch as the difference in the power to withstand the severity of our winters, may be owing to the more concrete state in which I suspect the sap is deposited in the tissue of the wood during winter, in mature, as compared with young plants. A further question arises here, whether woody plants, when once attacked, do not afterwards become more under the control of their parasite.

The first appearance of the fungus on Mr. Knight's pear trees, caused him no alarm, it being confined to spots on the leaves, but in after years the young wood also became affected, and perished.

The way in which parasitic fungi injure plants, is not, I believe, understood generally. They do not grow on the surface merely, of leaves, prevent perspiration, and. thus cause death. They spring from the living tissue and destroy it. What we see of the plant externally, is merely the fructification - the plant itself, composed of minute, thread-like filaments, spawn or mycelium, as it is usually called, is concealed in the tissue. Now the contents of the cells of plants are various, as researches recently made by the aid of chemical reagents indicate; the mycelium of fungi has the power of piercing the cell walls. By thus rupturing the tissue the contents are set free, they are no longer under the control of vitality, hence chemical action ensues, putrefaction of the part attacked follows, morbid matter is thus generated, which circulates with the fluids of the plant, and gives rise to further unhealthy action.

In this matter as on so many other points, a close analogy seems to subsist between the animal and vegetable worlds, the same law appears to prevail in both, that an unhealthy state of the larger plant as well as of the larger animal is the essential condition required for the attack and increase of parasites. "The different species of minute insects," observes Mr. Knight, "which feed upon the bodies of our domestic cattle, are scarcely ever seen, and never injurious so long as the larger animals retain their health and vigor; but when these become reduced by famine or disease, the insects multiply with enormous rapidity, and though they are at first only symptomatic of disease, they ultimately become the chief and primary cause. The reciprocal action of the larger plant and the mildew, upon each other, may be somewhat similar." (Knight's Phys. and Horticultural papers, p. 208.)

I apprehend no further remarks are needed to prove that this is, as you observe, an important subject of investigation, and I would suggest in conclusion, whether some Horticultural Society, or the Poraological Congress would not do well by instituting a searching and systematic inquiry with a view to ascertain what are the causes which lead to attacks of fungi, and by what means they can be prevented or modified. It is well to reward the successful improver of the pear and other fruits as our Horticultural Societies now do; but how much greater would be the service rendered to horticulture, how much more profitably would be the money expended, if a means could be discovered which would enable us to grow in a healthy condition, those varieties we already possess, or may hereafter obtain? If the inquiry should be confined to the pear alone; the first steps to be taken would be to determine the name of the fungi. A few fresh infected leaves hermetically sealed in a light tin case might be transmitted by post to the first authority on these plants in this country, and to two or three distinguished cryptogamic botanists of Europe - say the Rev. M. J. Berkeley of England, Professor Morren of Belgium, or Dr. Montague of France, not only with a view to ascertain the name of the parasite, but whether it exists in Europe, and if any means are there known to prevent its development or diminish it power.

A plain and accurate description of the disease should then be drawn up, and distributed with a series of inquiries, in different parts of the states to individuals likely to afford useful and accurate information. The returns would show the geographical limits of the disease, the period of its development and its intensity in different parts. I append a few inquiries which have occurred to me.

1. Has this disease been observed by you in the locality where you now reside, and if so, how long has it been experienced?

2. When once developed has it ever entirely disappeared, and under what circumstances?

3. Are seedlings more liable to be attacked than grafted varieties?

4. Among grafted varieties do any uniformly offer greater resistance to the disease than others?

5. What is the character of the soil of your orchard or nursery, and if there is any difference in the quality, texture, moisture or dryness of the soil, are trees more free from disease in one part than another, and if so, which?

6. State the position of your orchard, whether on low ground or on the side of a hill, and whether you have observed in the same locality trees to be more exempt from disease in one position than another?

7. Are teees growing in damp shady places more affected than those in moro exposed situations?

8. Does difference of aspect, as the north or south side of a hill, make any difference?

10. Have you tried trenching or deep plowing an orchard or nursery, or where pear seeds were sown, and with what results?

11. Have you mulched newly planted as well as established trees, and have these been more exempt from the disease than others in the same orchard not mulched?

12. In a locality where the disease exists, are pear seedlings always healthy if raised in new land?

13. Have you steeped pear seeds in any solution previously to sowing, and with what success?

14. Have you pared and burned the surface soil intended for the seed bed?

15. Have you dusted flour of sulphur on infested leaves or shoots, or inserted a portion in a hole in the stem, or applied a weak solution of sulphuric acid to the soil around a diseased tree and with what results?

16. Have you applied any special manure to your trees, which exercised any marked influence, beneficial or otherwise?

17. Have you observed the character of the weather immediately proceeding the development of the fungi, and whether in the same or different seasons their growth and increase seemed to be favored with peculiar atmospheric influences?

18. Have you tried any experiments with a view to cure or prevent the disease, or can you supply any additional information calculated to throw light on the subject, and which is not comprised in these queries? Respectfully, J. Townley.

Moundville. Marqusttt co., Wis.