Before again referring to the summer use of greenhouses, allow me to say a word or two upon the subject of correctly ascertaining the temperature.

In my last article upon this subject (p. 144, No. 3, Vol. 14) I say, I allow " the temperature to rise as high with solar heat as 80°," etc. This has been interpreted to mean, - and by those who should know better, - in the sun's rays. This is a very mistaken idea, and a very common one. Visitors are frequently surprised, upon an inspection of the thermometer in a southern exposure, at the apparent high temperature. I have noticed that the glass exposed to the sun will register from 10 to 20° higher than the actual temperature of the house. And this latter can only be correctly ascertained by suspending the thermometer in a shady place.

I have seen some of my professional brethren, I regret to say, so unreflecting, to say the least, as to imagine that turning the back of the thermometer to the sun was sufficient; not stopping to think that the black Japan of the case, by attracting the sun's rays, is a fruitful source of error.

A very simple contrivance is the use of a square post, (four to six inch, which may be made ornamental and used for climbers,) situate*d as near the centre of the house as possible, and about mid-way of which, on either of the four sides, as circumstances may require, the glass may be hung.

The above remarks are equally applicable to the temperature of vineries, etc.

And now, let me forestall an objection which may be raised to the article on the succeeding page of the same number. It will doubtless be urged that the vines will start before room can be made in the greenhouse for them. To this I answer, that no gentleman owning a vinery can do without a hotbed; and in this latter the grape-vines may be started, the steam of which will give them a capital start, swelling the buds and wood, so that when the greeuhouse is ready for them, they will be found to be quite advanced.

Before closing, allow me to make a suggestion about the application of manures to root crops. The prevalent custom is to mix with the soil, spading in; but I prefer putting it in the bottom of the trench. The philosophy of this is, that the roots seeking sustenance will grow straight towards the manure, and the result will be large, straight roots; while the reverse is the case when the manure is mixed with the top-spading. In some instances the roots will be large but more often forked. Tours respectfully, John C. Ure.

Chicago, April 5,1859.