This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
This tree ripens its seeds in June, giving the cultivator time to sow them and get the plants up the same season. The ripening of the seed is easily known by its falling from the trees. It may then either be swept up, or the gatherers may with ladders pluck the seed off the branches. The ground, should, of course, be ready to receive it, and then the seed should be sown immediately.
Alnus Cordifolia does not ripen its seed till late in the year; hence it requires to be gathered, cleaned, and kept till the following spring. As the seed is very small, it should be covered very lightly.
One point must be carefully attended to in raising such forest trees as have small seed. In dry weather it is absolutely necessary to water freely and regularly, for if the seed once sprouts and the soil is dry, the infant plant will perish.
I hope I have answered our correspondent fully and satisfactorily, and I trust such information will be acceptable and useful to many of our readers. I shall, at some future time, give similar directions on raising many shrubs from seed. - T. Appleby, in Cottage Gardener].