何首乌块根中异常结构的形成过程

何首乌的块根是一种常用的中药,块根内具有异常的次生结构。在块根的横切面上,自外至内依次为周皮、薄壁组织、排列成一圈大小不等的异常周韧维管束和中央维管柱。在块根形成以前,根的初生和次生结构都是正常的。以后,通常由围绕在初生韧皮纤维束周围的中柱鞘和次生韧皮薄壁组织细胞形成异常形成层,产生异常维管束。此外,还发现少数由中央维管柱分支而成。在块根膨大过程中,束内外以及维管柱次生木质部的薄壁组织细胞也分裂并增大。从而使块根中薄壁组织占80%左右。上述变化过程在不定根的中部开始,向上、下两

DEV ELOPMENTAL STUDIES ON ANOMALOUS SECONDARY STRUCTURE IN ROOT TUBER OF POLYGONUM MULTIFLORUM THUNB.

The root tuber of Polygonum multiflorum is a kind of chinese drug in common use.The secondary structure in it is anomalous.In the trans- verse section of a developed root tuber,it is composed,from outside to centre,of periderm,parenchyma,a irregular ring of anomalous amp- hicribral vascular bundles which are unequal in size,a centric vas- cular cylinder.The primary and secondary structures in the root are normal before it swells,In the latter development,anomalous cambium, which initial from the parenchyma cells of pericycle and secondary phloem around primary phloem fiber strands,differentiate anomalous vas- cular bunales in the most of root tubers,but the bundles in a few of them are developed by the branching of centric vascular cylinder.The pa- renchyma cells that are around the bundles as well as within the bun- dles and the xylem of vascular cylinder divide and expand during the swelling of root tuber,so 80% of volume in a root tuber is occupied by them.Because the development discribed above begins from the mid- dle of a slim adventitious root and proceeds in both acropetal and bas- ipetal directions along the root simultaneously,the shape of a root tu- ber usually becomes fusiform.The parenchyma cells in the root tuber are rich in starch grains.According to the experiments in histochemistry, when the anomalous cambia initial,the starch grains in their precur- sory cells reduce,and then disappear.After the anomalous bundles are formed,the starch grains are accumulated in their parenchyma cells. Also before and after wood ray cells in centric vascular cylinder divi- de,the changes in starch grains taking place in them are similar to tho- se discribed abvoe.