XEROMORPHIC CHARACTERS IN THE VEGETATIVE ORGANS OF PEGANUM HARMALA
骆驼蓬营养器官的旱生结构

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.