This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Polyanthuses may be parted at the end of this month: it would perhaps have been better had they been parted in May. When divided, be sure to plant them deep enough, so that the new fibres, which will come out just beneath the leaves, may at once enter the soil, instead of being exposed to the ravages of slugs, etc. In dry weather these troublesome insects take shelter beneath the foliage of the Polyanthus, and, if not looked after, will not only devour the young roots, but also eat holes in to the stems of the plants. Earthing up and frequent stirrings of the surface in hot weather will destroy numbers and prevent much mischief.