1892.] 



Embryology of Angiopteris evecta. 



473 



which, in one fortunate preparation, showed the first cap cell. The 

 other octant, together with the two posterior hypobasal octants 

 (which together form the rudimentary foot), ronnd off the base of the 

 embryo. The root presents considerable difficulty in tracing the 

 course of its development, as the apical cell, at no time very clear, is 

 early replaced by two cells, as I convinced myself by an examination of 

 sections specially cut obliquely in order to determine this point. More- 

 over, the root grows in a somewhat sinuous manner in the embryo, and 

 the cells of its apex may easily be confounded with other triangular cells 

 which occur irregularly scattered in the lower portion of the embryo. 

 It finally emerges, not immediately beneath, nor yet exactly opposite, 

 the cotyledon, but at a distance from it of between one-third and 

 one-half of the circumference of the embryo. The difficulties attend- 

 ing the exact following of its growth, added to the scarcity of 

 the material, have prevented my elucidating completely the details of 

 development, but the important point, that, even before its emerg- 

 ence from the embryo, its apex contains a group of initial cells occu- 

 pying the place of the single one characteristic of other orders of 

 Ferns, can be regarded as established with certainty. 



The vascular strand, which is differentiated early in the cotyledon, 

 joins on to that of the root, and the first tracheid appears in that part 

 of the bundle which is opposite to the junction of the cotyledon with 

 the stem, in fact, just at the point where the leaf- trace curves round 

 into the latter. Thence the further differentiation of the xylem 

 takes place in an upward and downward direction. 



When the embryo has reached a certain size it bursts through the 

 prothallium, the root boring through below, whilst the cotyledon 

 and stem grow through the upper surface. This manner of issuing 

 from the prothallium at once serves to distinguish Angiopteris from 

 those other Ferns whose embryogeny is known, and probably the 

 peculiarity of its growth may be reasonably connected with the 

 direction and position of the basal wall which separates the root and 

 short portions of the embryo. It will be remembered that in this 

 plant the basal wall is parallel to the plane of the prothallium, 

 instead of nearly at right angles to it, as in the leptosporaugiate 

 Ferns. 



Fresh leaves and roots speedily arise on the young plantlet, the 

 second leaf appearing just above the place of exit of the first root, 

 that is, not qoite opposite the first leaf. The third leaf rises 

 between the first and second ones, and nearer the first than the 

 second. Their roots observe the same rule of divergence as that 

 which obtains in the case of the first root. The stipular structures, 

 so characteristic of the Marattiacese, are entirely absent from the 

 first two leaves, but appear in a well-developed condition on the 

 third and all succeeding leaves. They fulfil the function of enclos- 



