植物的叶片是进行光合作用的主要器官。在植物一生中相继出现的叶片,在不同的生长发育时期担当着不同的功能。以小麦为例,上层叶的同化物大部分供给谷粒和茎;下层叶的同化物大部分供给根和分蘖;中层叶可向上下任何一个方向;或同时向两个方向供应同化物;而穗下的第一片叶——旗叶,几乎是谷粒碳水化合物的主要来源。可见旗叶是小麦最重要的叶片。作者曾试验,剪掉旗叶的小麦,秕粒增加,千粒重下降五至十克,与对照相比,减产三成左右。这个数字是相当惊人的:同时剪去的叶片随着叶序的增加,千粒重下降的越多。剪掉第一片叶子对产量几乎没有影响,剪掉旗叶下面的第一片叶子,千粒重下降一点五克。这里给农业生产者提出了一个很重要的问题,就是要特别注意加强对旗叶以及上位叶片的保护。为什么会这样?原来上位叶片的叶绿体数目多而且大,叶绿体内的基粒片层随叶序数增加而增加,旗叶最发达,因而光合效率高。这是上部叶片 Plant leaves are the main organs for photosynthesis. Leaves emerged one after the other in plant life, which play different functions during different growth and development periods. In wheat, for example, most of the assimilates in the upper leaves are supplied with grain and stems; most of the assimilates in the lower leaves are supplied with roots and tillers; the middle leaves can be in either of the up and down directions or the assimilates are supplied in both directions; The first leaf under the ear - flag leaf, is almost the main source of grain carbohydrates. Visible flag leaf is the most important wheat leaves. The authors have experimented with the flag leaves of wheat cut, increased grains, grain weight decreased five to ten grams, compared with the control, cut about three percent. This figure is quite amazing: at the same time cut the leaves with the increase of leaf order, the more grain weight decline. Cut the first leaf has almost no effect on yield, cut off the first leaf below the flag leaf, 1000 grain weight decreased 1.5 grams. A very important question for agricultural producers here is to pay special attention to strengthening the protection of flag leaves and upper leaves. Why is this? The original high number of leaf chloroplasts and large, chloroplast grana lamellar layer with increasing leaf number increased flag leaf the most developed, and thus photosynthetic efficiency. This is the upper leaf