摘要
众所周知,无论从系统发育或个体发育来讲,关于幼苗初生维管系统,特别是根茎过渡区的研究,对揭示与阐明被子植物的起源和演化都具有十分重要的意义。近百年来,在这方面已积累了大量资料。归纳起来,大致可以分成三大类,本文谨择其具有代表性的学派观点进行介绍,以供从事这方面研究者的参考。
As everyone knows, hypocotyl, so-called root-stem transition region,was generally considered as an insurmountabale barrier in the study of theprimary vascular system of Angiosperm. The order of the traditional discr-iption of the vascular system was from root apex through hypocot l to sho-ot apex (Eames and MacDaniels, 1947; Lenoir, 1920.). Though some rese-archers considered that the vascular system of the seedling was originallynot continuous (Dangeard, 1889, 1913) or suggested that double origins (end-ogenous and exogenous) existed in the development of the vascular systemof seedlings (Thoday, 1939), they did not pay attention to the existence ofCNZ and its significance in the study of phylogeny of the primary vascularsystem of angiosperms. Therefore we do not agree to the viewpoint that theseedlings of angiosperms is divided into two parts: roothypocotyl-cotyledenand epicotylary shoot (Esaw, 1953). We maintain that the seedling ofangiosperms should be divided into three parts: hypocotyl-root zone; CNZand epicotylary shoot zone. We think the research methods mentioned above is contrary to the fo-ssil plants discovered and the ontogenic process of the modern Angiosperm.From the phylogenic point of view, stem developed first and root after; formthe ontogenic point of view, active shoot apex and inactive root primordi-um occured as early as the cordiform embryonic stege. When embryo axiswas vissible after the further development of embryo, there existed a cons-ervative CNZ between shoot apex and root primordium. The haplostele inshape of the primitive protostele still remained in this zone. Later, hypoc-otyl developed from the lower part of CNZ and root from the end of hyp-ocotyl. Hypocotyl was the cotyleden node-root transition region. In themiddle and upper parts of CNZ, namely, the part above the plate shapeshowed by the combination of two cotyleden traces, an meristimatic tissue-cotyleden node-stem transition region remained, where the differentiation ofcells was slow. In R. japonicus, the embryonic tissue differentiated into thevascular tissue only when the growing tip changed from the vegetative shootapex into the reproductive shoot apex after several foliage leaves developedon the growing tip. This vascular tissue connected with the vascular tissueof the stem above and the vascular tissues of the lower part of CNZ, hyp-ocotyl and root bellow to form the whole of the primary vascular system ofthe seedling. Thus it can be seen that the origin and evolution of the prim-ary vascular system of the seedling. Thus it can be seen that the origin and evolution of the primary vascular system of the stem do not relate to hyp-ocotyl and root. Therefore the traditionalmethod discribing and studying theprimary vascular system of angiosperms from root through hpocotyl to stemshould be discarded. The new method discribing and studying the primaryvascular system from CNZ to both up and low ends (shoot apex and rootapex) should be put int use. Studies showed that the evolution of the steleconformed to the telomic theory and related to the direction of the differ-entiation of metaxylem (Zimmermann, 1956).
出处
《植物研究》
CAS
CSCD
北大核心
1991年第3期85-90,共6页
Bulletin of Botanical Research
