Students' handbook to accompany Plants and their uses . ch can resist con-ditions of extreme drought,are called ./<r<y<////^.s. The onlv wav in which one can geta good idea of the o difference betweenxerophytes and ordi-nary plants, or meso-jiliiitf*. intheirpowerto endure a combi-nation of high tem-perature and scantyAvater supply is tocompare their behav-ior under conditionsof drought. A pottedplant such as a cactusor a houseleek for arepresentative xero-pliyte, and a youngbean plant or mus-tard plant for a typical mesophyte, it left unwatered, will affordmaterial for a highly profi
Students' handbook to accompany Plants and their uses . ch can resist con-ditions of extreme drought,are called ./<r<y<////^.s. The onlv wav in which one can geta good idea of the o difference betweenxerophytes and ordi-nary plants, or meso-jiliiitf*. intheirpowerto endure a combi-nation of high tem-perature and scantyAvater supply is tocompare their behav-ior under conditionsof drought. A pottedplant such as a cactusor a houseleek for arepresentative xero-pliyte, and a youngbean plant or mus-tard plant for a typical mesophyte, it left unwatered, will affordmaterial for a highly profitable comparison of types. Are any xerophytes of economic value? any mesophytes?any water or marsh plants? (Jive as many examples aspossible. 81. Advantage of shedding leaves. When the soil tempera-ture is nearly at the freezing point, most plants are unable toabsorb much water by their roots. It is probably owing mainlyto this fact that our ordinary irintcr <l<;-nlnnnx trees have theirhabit of shedding their leaves at the approach of winter. If. Euphorbia splendciis Hit is rather leafy when wellapplied with water hut nearly leaf-when forced to live with avery scanty water supply less THE STEM AND THE LEAF 83 their actively transpiring leaves were to remain at work whilethe ground was almost or quite frozen, the tree would suffera fatal loss of water. It has been found that the larch (which sheds its leaves) ismore resistant to such conditions than are most of the ever-green conifers, although the latter have leaves of a highly xero-phytic type. In a rainless summer some shrubs retain or shedtheir leaves in proportion to the amount of soil moisture withwhich they are supplied. The Euphorbia splendens (fig. 67) isa commonly cultivated plant which well illustrates this capac-ity to adjust the amount of leaf surface to a varying moisturesupply. In regions like Southern California and the coast ofthe Mediterranean, where the long, hot summers are nearlyrainless, some trees an
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Keywords: ., bookcentury1900, bookcollection, bookdecade191, booksubjectbotany
