534 



A TEXTBOOK OF THEORETICAL BOTANY 



metre in total spread, but it is compound and two to three times pinnate 

 (Fig. 531). Each pinnule is shortly stalked, lanceolate in outline and measures 

 2 to 3 cm. broad by 15 cm. long. Each pinnule has a strong midrib with 



Fig. 531. — Marattia froxiuea. Part of a fully 

 developed leaf. The original is about i metre 

 across. 



free lateral veins, which fork once, each fork supplying a sorus near the 

 margin. At the base of each petiole there are two thick stipules, which are 

 generally united (Fig. 532). The leaves are eventually separated from the 

 stem by an abscission layer just above the stipules, which remain attached 

 as a permanent covering of the old stem. 



The petioles of Marattia have a large number of leaf trace bundles 

 arranged in a complex pattern, which is fundamentally that of an arch with 

 its open side towards the stem. Only two bundles enter the leaf base from 

 the stem (cf. Cycas, p. 716), each with a single central protoxylem, and the 

 numerous meristeles of the petiole are produced by the branching of these 

 two. 



Anatomy of the Stem and Leaf 



The stem apex shows a meristem, not a single apical cell, though there 

 is some evidence that a group of four apical cells is involved in the formation 

 of the meristem. A single apical cell exists only in the sporeling. 



The stem of the sporeling is protostelic, but in the mature stem there is 

 a very complex polycyclic dictyostele of numerous small meristeles, which 

 is rendered more complex by the frequency of commissural strands linking 



