骆驼蓬营养器官的旱生结构

 骆驼蓬是生长在荒漠或盐碱地区的旱生植物，具有显著的旱生结构特征。主根粗壮，其中柱周围产生2或3轮呈同心环状排列的异常维管束。这种异常结构对旱生植物具有重要的生态学意义。茎肉质，其皮层、韧皮部，尤其是髓内具有发达的贮水薄壁组织细胞。叶片肉质，光滑无毛。其表皮细胞的外切向壁有较厚的角质层，表面具皱纹状突起。气孔器与表皮细胞平齐，面积较大，而密度较小。栅栏组织发达，为环栅型，包围着发达的贮水组织。叶脉维管束不发达。其叶表面积与体积之比远比中生植物小。根据以上营养器官形态结构特征，可以认为骆驼蓬是典型的多浆汁旱生植物。

XEROMORPHIC CHARACTERS IN THE VEGETATIVE ORGANS OF PEGANUM HARMALA

Peganum harmala, a xerophyte, growing in extremely dry habitats or in salt marshes possessed distinct xeromorphic characters. The thickened tap root appeared to consist of 2 or 3 rings of anomalous vascular bundles surrounding the central cylinder which might be an important adaption to dry condition. The succulent stem was characterized by a well-developed water-storing tissue in the cortex, phloem, especially in the pith. Leaves were also succulent without trichomes. The outer walls of the epidermal cells were covered by thick cuticle whose surface was ridged. The guard cells of the stomata were at almost the same plane level with other epider- mal cells. The stomatal size was larger and its frequency was lower than those of other xerophytes. Two types of tissues could be distinguished in mesophyll: palisade tissue and water storage tissue. The veins in the leaves were not so developed. Ratio of the external leaf surface to its volume was smaller than mesophytes. According to the structural features mentioned above it can be concluded that Peganum harmala is a typical succulent xerophyte.