THE HOMOSPOROUS LEPTOSPORANGIATJE 



39i 



e. g., Alsophila contaminans, the trunk is quite free from roots, 

 and the leaves fall away, leaving very characteristic scars 

 marked by the vascular bundles. In others, like Dicksonia ant- 

 arctica, the whole trunk is covered with a thick mat of roots, 

 thicker than the trunk itself. 



The prothallium is exactly like that of the Polypodiacese, 

 so far as it has been studied (Bauke ( i) ), except that in some 

 species of Alsophila there are curious bristle-like hairs upon the 

 upper surface. In the structure of the antheridia the Cyathe- 

 acese are intermediate in character between the Polypodiacese 

 and the Hymenophyllaceae. The characteristic funnel-formed 



A, 



FIG. 229. A, Part of a sporophyll of Thyrsopteris elegans, Xz; B, section of the 

 sorus, Xio; C, leaflet, with two sori, of Cyathea microphylla. (A, B, after 

 Kunze; C, after Hooker.) 



primary wall of the former .occurs here, but not until one and 

 sometimes two preliminary basal cells are cut off, as in Os- 

 munda or Hymenophyllum. The following divisions corre- 

 spond exactly with those of the antheridium of the Polypodi- 

 aceae, except that Bauke states that the cap cell, as well as the 

 upper ring cell, may divide again. The dehiscence is effected 

 either by the separation of an opercular cell or by the rupture of 

 the cap cell. The archegonia are like those of the Polypodi- 

 acese. In Cyathea medullaris Bauke figures a specimen, how- 

 ever, where the neck canal cell is divided by a membrane (1. c. 

 PI. IX, Fig. 8). 



The first divisions in the embryo correspond with those of 

 the Polypodiaceae, but the further development of the young 

 sporophyte is not known. 



