This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Noticing what you said in the last Gardener's Monthly about the fertilization of the Yucca, I thought you might be interested in knowing that I have gathered seeds of angustifolia for three years past. Last year and the year before, I only found it producing seed at one place, on Bear Creek. I have before found it in bloom upon the high plains. I have attributed my failure to find it there the past two years to the dryness of the seasons, and that where I have found it the roots penetrate through the sandy soil upon which it grows into the decaying rock beneath, where there is always considerable moisture, and, I should think proper nourishment for such plants. As to the Pronumba yuccasella, I have-invariably found a great portion of the seed destroyed by some worm eating through the centre of them, and I have noticed the holes where it eats into or out of the pods, but I have never seen the insect, nor do I remember now whether or not every pod was more or less eaten, but that is my impression now.
I think, however, that sometimes only one or two of the cells would be eaten out, sometimes wholly and sometimes only partially, leaving in some pods most of the seed good, and in others only a few.
I had the opportunity last summer, in excavating for our new city water works, of seeing just how some of those plants which grew so luxuriantly on our parched plains, get their nourishment. I found Yucca angustifolia and Ipomoea leptophylla invariably sending their roots down through the soil of clay and loam, through the sub-soil of sand and into the decaying rock beneath, where they evidently obtain the nutriment necessary to their growth. This rock along the line of our works (over three miles in length) was generally found at a depth of from three to five feet, and was quite decomposed on top, so that there was no difficulty in plowing it to the depth of from one to three feet; and in this rotten bed-rock I found the fibrous roots spreading out and penetrating to the depth of from one to two feet.