In section (60. Spring-planted Cuttings) the reasons why grape and other cuttings are put in solar hot-bed in inverted position are given. If most heat is given at the base of the cutting it favors the emissson of roots, while the top buds are relatively dormant. In the same way if green cuttings are inserted in sand warmer than the air above, it favors the more rapid callusing and rooting of the base, while the parts in the air show less active cell formation. Even rooted plants in the open air during the growing season are in most if not all countries favored with a warmer soil than the average temperature of the air. But as stated in (19. Root-protection), exposed soil in interior climates often gets much hotter than the air. In this case the branches and leaves will give off moisture faster than the roots can supply it. In the same way the soil of the cutting-bench may get too hot under artificial conditions as well as too cold.