5io 



FILICALES 



and Angiopteris (Fig. 278 A and c) : or they may be more extended along 

 the veins, as in Archangiopteris (Fig. 278 B) : or they may occupy the 

 whole space from margin to midrib, as in Danaea (Fig. 278 E). But in 

 all these oases the disposition of the sorus is essentially the same, and 

 the differences those of detail only. In Kaulfussia, however, the sori are 

 dotted over the broad under-surface without apparent order, a condition 





FIG. 279. 



Vertical longitudinal section of the stem of a young plant of A ngiopteris evecta. b = the 

 youngest leaves still quite covered up by the stipules, nb ; si stalk of an unfolded leaf 

 with its stipula, nb ; , everywhere the leaf-scars on the basal portions/^ from which the 

 leaf-stalks have separated ; c, c, the commissures of the stipules in longitudinal section ; 

 w, zy, the roots. Natural size. (After Sachs, from Goebel's Outlines.') 





which appears widely different from the rest (Fig. 278 D) : but comparison 

 of leaves of Danaea, and especially of those which are only partially 

 fertile, gives the clue to an explanation ; for there the normally elongated 

 sori are found to show occasional fissions, and the partial sori, with 

 circular outline like those of Kaulfussia, appear isolated upon the enlarged 

 leaf-surface (Fig. 281 a, b, c). It seems probable that the condition of 

 Kaulfussia was acquired during descent in some such way as this, on the 

 gradually broadening leaf. The frequent occurrence of sori showing similar 



