一、“死”证法 在学校植物园里选择一株木本植物,在其主茎相距一定宽度环割两圈,深度以到形成层为止,剥去圈内树皮,刮去木质部上的形成层。树皮环割后,割断了韧皮部的筛管,使叶同化的有机物运转受阻。所以,经过一段时间后在环割的上端切口处聚集许多有机物。这些有机物促进环割处形成愈伤组织,即节瘤。如果环割过宽,虽然叶仍可获得木质部导管输送来的水分和无机盐,但根系不能获得叶同化的有机物,时间一久,根会饥饿死亡。这便是“树怕剥皮”的道理。这一道理证明,韧皮部的筛管 First, the “death” method selects a woody plant in the school botanical garden, and cuts the main stem two times apart at a certain width, until the depth reaches the formation of the layer, peels off the bark inside the circle, and scrapes off the formation of the xylem. Floor. After the bark was cut, the screen of the phloem was cut off and the operation of the organic assimilation of the leaves was hindered. Therefore, after a period of time, many organic substances accumulate at the upper cut of the ring cut. These organisms promote callus formation at the circumcision, that is, nodules. If the circumcision is too wide, although the leaves can still obtain the moisture and inorganic salts from the xylem conduits, the root system can not obtain the organic assimilation of leaves, and for a long time, the roots will die of starvation and death. This is the reason why “trees are afraid of skinning.” This truth proves that the screen of the phloem