This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The mulberry has male and female flowers in separate flowers on the same plant. But different trees vary in the proportions of each - some trees having wholly male flowers. Morus multicaulis is a variety of Morus alba, almost always with male flowers - always, for anything we know. Hence it never seeds, but is propagated wholly by cuttings. Some years ago it became infested with a disease similar, if not nearly the same as infests the American Plane or Sycamore, and this disease continues to this day. Silk worms fed on these leaves become diseased. This was the chief reason of the failure of the old "Multicaulis" scheme. The seedlings of Morus alba are usually free from disease, and make healthy food for the silk worm. Although Morus alba signifies white mulberry, the fruit is sometimes black or amber color. Morus Morettii is but a variety of this species, as also is the Russian or Mennonite mulberry of the West. The danger is that in propagating these from cuttings or layers, some disease may be also propagated.
We should recommend those having the interests of silk culture at heart, to rely chiefly on seedling white mulberry.