南湖菱根系的研究

A STUDY ON THE ROOT SYSTEM OF TRAPA ACORNIS NAKAI

南湖菱的根包括胚根、不定根以及由不定根生出的次生根。胚根具有背地性生长,生活期短。不定根有两种:一为吸收根,它具很发达的通气组织,另一为漂浮根,在其皮层组织内含丰富叶绿体。漂浮根发生于茎节的中柱鞘细胞,它有发育良好的根冠,表皮细胞不分化为根毛,中柱初生木质部为四原型,发育方式为外始式,维管束中的木质和韧皮两部分相间排列,整个器官属内起源,可以说明这一漂浮器官是根而非叶。次生根系由两个部分组成,即内皮层相应的细胞形成根冠,而中柱鞘细胞分裂形成根的表皮、皮层与中柱。次生根对着漂浮根本质部束向外生长,其结构与漂浮根相仿佛,只是各区层数较少,结构简单。

Radicle, adventitious roots and lateral roots constitute the root system of Trapa acornis. The radicle grows nagative geotropically with a very short life duration. Adventitious roots are of two types, one of which is the absorptive root which is well developed and grows deep into the mud of water bottom for anchorage being considered as the main organ for absorbing water and mineral nutrients from the mud; the other is floating root with well developed chloroplasts in cells of its cortical tissue.Floating root of Υ. acornis is initiated from the pericycle of the stem node. It has a well developed root cap with no root hairs developed from its epidermal cells. Stelar structure is tetrarch with pri- mary xylem elements in exarch development. Xylem and phloem strands are arranged in alternate. order. By the fact that such floating organs originate endogenously with all the structural characteristics mentioned above coincide with that of a root, it may be quite reasonable that such organs can be considered as roots instead of leaves.The floating root may develope lateral or secondary roots which originate from cells of two parts of the floating root, namely cells of endodermis and cells of pericycle. The former develope into the root cap and the latter differentiate into epidermis, cortex and stele. The position of lateral root is against the protoxylem ray. Structure of lateral root is similar to that of the floating root, but is comparatively much more simpler.