We take it for granted that every "constant reader" of the Gardeners' Monthly knows by this time that the hardiness of trees is not a question of temperature merely, but that the hygrometer as well as the thermometer has to be consulted. It is amazing that what we have gathered for our readers travels so slow in the Old World, that few of its intelligent inhabitants can understand it. One of the most advanced of Scotch botanists in attendance on the recent Science Convention in Philadelphia, was amazed to see the liriodendron "hardy" in the woods, when told that the thermometer sometimes went down 1o° or 200 below zero, while it was " often injured at 200 or 300 below the freezing point in Scotland."