164 



PRINCIPLES OF PLANT-TERATOLOGY. 



of anther-formation, there are other possible methods 

 to be considered. 



For example, and this in itself would, cause forking 

 of the leaf, the apex might have become infolded, for 

 a longer or shorter distance,* on to its upper surface, 

 fusion of these two upper surfaces along the midrib 

 subsequently occurring. Such an apical infolding was 

 actually observed in a foliage-leaf of Saxifraga ligulata 

 (PI. XLIII, fig. 13), but in this case there was no fusion 

 of the surfaces. It can be seen that such an infolding, 

 combined with facial fusion, would account for the 

 structure of the upper part of Celakovsky's Hieracium- 

 leaf, and would inaugurate incipient dichotomy of the 

 leaf-apex. Another method, which might or might not 

 be combined with that just described, would consist 

 in the fusion of two upturned basal lobes across the 

 upper face of the leaf in such a way that the upper 

 surfaces of the leaf and the basal lobes were opposed, 

 giving rise to such a structure as the basal part of 

 Celakovsky's Hieracium-\e?d. The basal lobes of a 

 sagittate or hastate leaf might be regarded as resulting 

 from the dichotomy of the basal part of a peltate leaf, 

 or the latter as the result of fusion of two such lobes. 

 If now we imagine the basal part becoming adpressed 

 to and fused by the midrib of its upper surface with 

 that of the leaf along its midrib, the resulting structure 

 would be the two required lamellae, which might fuse 

 with the two descending from above, and in that way 

 yield us the anther-structure; but the basal lobe might 

 be sufficiently long to fuse with the leaf along its entire 

 length, when no infolding of the apex would be neces- 

 sitated, f There was observed in Galtha anclicola an 

 infolding of the leaf-base on either side of the midrib. 



* Yet this is, after all, only a variant on the first method. 



f Cf. the leaves of Buddleia Hemsleyana and Saxifraga ligulata described 

 in Vol. I. The structure and interpretation of the Hieracium-le&f exactly 

 confirm and agree with the view (arrived at independently) set forth in 

 Vol. I that these "enations" and invaginations, etc., of foliage-leaves really 

 represent stages in the dichotomy of the leaf into two, or in the fusion of 

 two leaves into one. And this view may be applied also to the structure 

 of the anther. 



