200 GLEICHENIACEAE [ch. 



conduction, and the vascular system differs accordingly, though still the 

 underlying Gleicheniaceous scheme may be traced (Fig. 482). The general 

 stelar structure of this Fern has been already described, with its internal 

 sclerotic pith which fluctuates in bulk, and its inner endodermis which is 

 of inconstant occurrence, and connects at no point with the outer endodermis 

 (Vol. I, p. 132, Fig. 125). A transverse section of the stem is seen in Fig. 

 483 A, while the origin of the leaf-trace of one of the larger leaves is shown 

 in Fig. 483 B, C, to be typically that of protostelic Ferns. The natural inter- 

 pretation of this structure is that Platyzoiua is a Gleicheniaceous Fern of 

 rather advanced type, but still imperfectly solenostelic, in which the departure 

 of the relatively small leaf-traces causes only a local disturbance of the 

 medullated stele. The petiolar bundle is of a reduced C-form and especially 

 so in the minute sterile leaves. 



The other outstanding Gleicheniaceous type, Stromatopteris, is still a 

 problem, since its anatomy is imperfectly known : we still await a detailed 

 description of the underground parts. Compton has, however, recorded 

 "the existence of a horizontal rhizome, buried in the soil to a depth of 

 3-4 inches, and giving off erect branches which fork repeatedly in an 

 irregular fashion. Roots are borne sparsely on this horizontal rhizome" 

 (Compton, /c'wr;?. Linn. Soc, xlv, p. 453). So far as the anatomy could be 

 worked out from dry material, there is now reasonable information as to the 

 upward-growing shrubby lateral branches from the rhizome of the plant 

 (Fig. 484). This consists of cylindrical, dichotomously branching axes 

 bearing, without any apparent regularity of position, long simply pinnate 

 leaves. Transverse sections of these axes reveal a simple protostele with 

 parenchyma-cells scattered through the xylem, a peripheral phloem, peri- 

 cycle, and endodermis. Moreover sections at a forking indicate dichotomy 

 (Fig. 485 a). In fact the characters are those of the Gleicheniaceae, except- 

 ing the erect position. The apices of these axes appear to be soon arrested. 

 The petiolar supply at its base may resemble very nearly that of the axis: 

 but higher up it is clearly of the C-type, and as it pursues its course into the 

 pinnate region the minute pinna-traces are given off in extra-marginal 

 manner, as in Gleichenia (Fig. 485 U). Pending more detailed information 

 these shrubby upward-growing regions may be held to be erect forking 

 rhizomes bearing simply pinnate leaves. 



On these anatomical facts two views are possible. Either that the proto- 

 stelic state of most Gleichenias is primitive, and that the solenostelic type 

 has been derived from it: or that the protostelic types are reduced from a 

 solenostelic ancestry. The former view appears the more probable in so 

 primitive a family : and especially in view of the fact that G. pectinata, which 

 is solenostelic, has sori and sporangia of a character advanced in the direction 

 of the simpler representatives of the Cyatheaceae, which are solenostelic or 



