COENOPTERIDACEAE 



[CH. 



creeping rhizome (see Vol. I, Fig. 122, p. 128). Many of the Zygopterideae 

 appear to have had a lax form of shoot. Dr M. Benson has observed in 

 Metaclepsydropsis how the same creeping rhizome, followed through 22 inches 

 of its course, bore only five leaves within that distance. Its habit must have 

 been very like that of Pteridiuvi. 



On the other hand, where the axis is massive and upright, with short 

 internodes and crowded leaf-bases, a different structure may be found which 

 is, however, related to that corrugated form seen in Ankyropteris. An ex- 

 treme example of it has been described in detail with beautiful plates by 

 Prof P. Bertrand in Asterochlaena laxa Stenzel, a plant of Permian Age. 

 The upright axis increased conically upwards to 5 cm. in diameter. It was 

 covered by the bases of the closely crowded petioles together with roots. 



X , 



(SO ^ i Xx/i "Ny®® IX 



Fig. 322. Asterochlaena laxa. General transverse section, showing the 

 stellate stele, with bilobed or trilobed arms, and the leaf-traces, but 

 only the inner petioles. The Roman numerals indicate the leaves of two 

 successive whorls. .A" = roots; 6"= pinna-traces. (Slightly magnified.) 

 (After Dr P. Bertrand. From Scott.) 



The phyllotaxis was on a complicated plan with a tendency towards verti- 

 cillation (Fig. 322). Centrally in the transverse section is a large stellate 

 stele measuring 5 mm. or more in diameter, with some 7 or 8 diverging rays, 

 each more or less lobed at the periphery. It is from these lobed arms of the 

 star that the leaf-traces are abstricted, each lobe giving rise to two or three 

 traces but occasionally to only one. It thus appears that the number of arms 

 of the star bears no constant relation to the number of the leaf-traces. This 

 condition is comparable with what is seen in Lycopodium, where the small 

 leaf-traces do not correspond in number or in arrangement to the rays of 

 the stellate xylem (Jones, Trans Linn. Soc. Vol. vii, Part II, 1905). 



