慈姑不定根中导管分子的观察

OBSERVATION ON VESSEL MEMBERS IN THE ADVENTITIOUS ROOT OF SAGITTARIA SAGITTIFOLIA L.

慈姑导管仅在根中出现。根的后生木质部中央导管由顶端平截、单穿孔的网纹导管分子连接组成;周围较小的导管分子和管胞有从梯纹管胞向导管分子演化的各种过渡类型;有一至多个梯形穿孔或单穿孔发生在导管分子的端壁或侧壁,并有分枝型导管分子存在,特别在根与主茎连接处尤为明显。管胞亦有分枝与不分枝的类型。

Vessels are found in the xylem of adventitious root of Sagittaria sagittifolia only. The root xylem consists of a large central vessel surrounded by strands of small vessels and tracheids at its periphery. The large central vessel is formed by short, wide and truncate vessel elements with simple perforation. Other tracheary elements show various types of differentiation. The evolutionary sequences of vessel member begin with long scalariformly pitted tracheids, these tracheids are succeeded by vessel members of long and narrow shape with tapering ends. The cells become shorter and wider progressively with their end walls less inclined and finally being truncated. Perforation plate of the primitive types is scalariform with numerous bars, increased specialization results ina decrease the number of bars to total elimination forming a simple perforation. Perforations may be present at each end and also on the side wall.