【摘要】 <正> 一、引言慈菇^**在分类学上隶属于泽泻科。为一种普通的水生植物,分布于世界各地。这种植物因为生长容易,繁殖迅速,往往可以在河湖水边,形成大片的面积。在我国南北各地,沼泽河湖水多的地方,亦常有生长。更有的,在水稻田旁水池洼沟里,加以培植,采收块茎（慈菇）,用作蔬菜,或者利用来作淀粉的原料。根据旧书藉记载,此重块茎还有药用的更多还原

【Abstract】 A series of investigation concerning the formation and development of the various organs in Sagittaria sinensis Sims,a common water plant,has been undertaken.The present paper deals only with a study of the formation and differentiation of its root system. The tuber which we utilize as food is the swollen apex of a stolon.The elongated terminal bud in the tuber exhibited nodes and internodes in early stages of development,and the adventitious roots were vigorously grown around the third node from the base of the bud.In the transverse section of the third node the roots became radially arranged.These roots,as in most of the water plants,possessed no root hairs.Instead,there were numerous minute secondary roots.The stolons which appeared at a more advanced stage were intermingled with the adventitious roots as the bud continued to extend. The adventitious root originated from the meristematic cells peripheral to the procambium,forming a group of cells distinct from the surrounding parenchyma cells.It became conical shaped after several cell divisions and three layers could be identified:these were initials of root cap (calyptrogen),initials of cortex and epidermis and initials of central cylinder. Later on the cells of the middle part of calyptrogen began to divide periclinally and anticlinally;while the peripheral cells undertook anticlinal divisions only.The initials of cortex and epidermis maintained the uniseriate condition in the middle portion,while the peripheral cells of this layer divided vigorously. In each division a small and a large cell were formed.The outer small cell became the epidermal cell and the inner large one continued to divide into cortical cells,which were very regularly arranged.The outermost two layers of the cortex,i.e.the exodermis,together with the epidermis,later formed a special thick layer.Many scattered secretory cells were differentiated from the cortical cells and later intruded into the exodermis.The cells in the central cylinder were also arranged orderly.The phloem appeared first,and was followed by the development of vessels.The"central cells"were large and usually divided transversely.The cells at the base of a root gradually joined the procambium cells of the young stem. In a mature root,the root cap consisted of about ten layers of cells of which four zones could be recognized,i.e.surface zone,central zone,peripheral zone,and calyptrogen.Only the cells of calyptrogen still sustained the ability of mitosis. The cells of initials of cortex and epidermis gradually decreased in number until there were only two or three cells.In transverse section the matured secretory cells imbedded in the exodermis appeared as groups of four cells, rhombic shaped,with a large central cavity.Later the combined layer of the epidermis and the exodermis became suberized and shrunken.Among the cortical cells,of which many were binucleate,there were large intercellular spaces forming the conspicuous aerenchyma.In the innermost layers the cells were compactly arranged with no visible intercellular spaces.The endodermal layer, although obscure in the immature part,became distinctive at the base of the root by the presence of the Casparian strip. The pericycle consisted of large isodiametric cells which usually became differentiated into the initials of the secondary roots.The differentiation and maturation of the vascular tissues in the cylinder were similar to that of other higher plants.The"central cells"enlarged tremendously and occasionally segments of double row of cells were seen in the longitudinal sections. Secondary roots were formed at early stages of development of the adventitious root.In transverse sections the earliest detectable initials of the secondary roots consisted of three enlarged cells.The middle one of these cells divided periclinally at first,from which the outer daughter-cell accompanied the other two large cells to form the initials of cortex and epidermis,whereas the inner one gave rise to the initials of central cylinder.The neighbouring cells in the endodermis differentiated simultaneously to become the calyptrogen of the secondary roots.Thus,the secondary roots were originated from two different kinds of tissues,the endodermis and the pericycle.Further differentiation and maturation were similar to the development of adventitious root in this plant.更多还原