138 PHILOSOPHICAL NOTES ON 



from the upi3er leaf. On these grounds, and in the light of this 

 comparative study, it is concluded that the recognition of the 

 phyllopodium,* and tre^itment of the whole leaf, as a simple branch, 

 or as a branch sy stein, is in accordance with the true nature of the 

 leaf, as seen in all vascular plants ; while at the same time, if this 

 method were adopted, the whole shoot (or developed bud) would 

 then be subjected to consistent morphological treatment, since the 

 relation of the plnncB to the j)hyllopodiu)n is similar to that of 

 the xchole leaf to the axis, which bears it." 



The bud in growing and develojiing itself would sub-divide 

 into leaves, and the phyllopodium of each leaf would sub-divide 

 into pinna?, or, in other words, the shoot divides into axis and leaf, 

 and the latter into phyllopodium (which is an axis) and pinna3 

 (which are smaller leaves). 



What clearer exposition of the morphological nature of the 

 leiif is needed in spite of the accompanying unnecessary technical 

 terms ? The leaf is a branch like all other branches, and the 

 pinna or leaflet is to the midrib what the leaf is to the main stem. 



^N^othing can more clearly shoAV the identical nature of the 

 midrib and stem than the case of reversion quoted and pictured by 

 Dr. Masters in his " Vegetable Teratology," p. 88, where the main 

 flower stem of a Gesnera has reverted to a midrib, and the flower 

 peduncles to leaf veins — all fasciated into a leaf by means of the 

 mesophyl ! This shows that the midrib of the leaf is homologous 

 with the main stem of a plant, and the leaf veins homologous with 

 the sub-divisions or petioles of that stem. 



Lindley, in his " Veg. Kingd.," p. 223, says that Miquel regarded 

 the leaf of Cycads as a sort of branch, so that the Cycad ovules 

 would really be homologous with axillary buds. 



Goebel (" Outlines of Classif.," p. 209) considers the stem of 

 Lygodium among ferns to be the midril> of an indefinite leaf, its 

 apex growing for a long time after the lower pinnae are fully 

 develoi)ed, as in the case of Xephrolepis, and others. Those 

 parts of Lygodium which were considered leaves, are only pinna3, 

 which go on repeating themselves indefinitely in the same form. 

 The apex of each leaf-like division remains like a dormant 

 terminal bud, while the midrib continues to lengthen indefinitely, 

 and becomes the main stem, and gives off similar leaf-like divisions 

 or compound pinna?. 



* Petiole and midrili. 



