Mr. F. O. Bower. On the Leaf of the [May 2), 



tnrbnnce of their arrangement, resulting from peculiarities of the dis- 

 tribution and localisation of growth, are regarded as of but secondary 

 importance. In treating of the leaf, however, this principle is not 

 kept in view. The very distinction of foliar base and upper leaf is 

 chiefly based upon results of intercalary growth which would be 

 regarded as but of secondary importance in treating of the shoot 

 at large. One of the objects of the investigations detailed in this 

 paper was to ascertain, by comparative study of the lower forms, 

 whether there is sufficient ground for this inconsistency of treatment. 

 It is further pointed out that, though this treatment is not open to 

 obvious objection in the case of simple leaves, in branched leaves the 

 parts thus distinguished are not morphologically co-ordinate. On 

 dividing the leaf into foliar base and upper leaf, a distinction is 

 drawn between the lower part of the axis (so to speak) of the leaf 

 and the whole of its upper branch system a distinction which might 

 be compared with that of the bole of a forest tree below the lowest 

 branches from the whole of the upper part of the trunk with its 

 branches of all orders ; such a distinction would not lead to a true 

 knowledge of the morphology of the tree, or of the relation of its 

 parts one to another. It is found that a comparative study of the 

 leaf of the lower vascular plants does not justify the continuance of 

 this inconsistency in the method of treatment of axis and leaf, but 

 rather that the leaves of the lower forms lend themselves to a con- 

 sistent treatment throughout their length as branch systems. As we 

 rise in the scale, the main axis of the branch system becomes gradu- 

 ally more differentiated as a supporting organ, distinct from the 

 members of higher order which it bears, while the assimilating func- 

 tion chiefly devolves upon its flattened branches. 



This being the case, this axis must be recognised by a distinct 

 term : the name phyllopodium is proposed to designate the main axis of 

 the leaf exclusive of its branches (pinnae) ; thus the relation of the 

 pinna to the phyllopodium is similar to that of the leaf to the axis. 

 Three parts of the phyllopodium may be distinguished in complicated 

 leaves, but this distinction is only to be drawn where a difference 

 really exists ; the basal portion may be called the hypopodium, and 

 coincides with Eichler's " blattgrund ; " the mesopodium is the equiva- 

 lent of the petiole ; the third part, or epipodium, differs from the 

 " oberblatt " of Eichler in including only the upper part of the phyllo- 

 podium, exclusive of its branches. This method of treatment of the 

 leaf is consistent with the treatment of the stem, while the parts 

 severally distinguished are morphologically co-ordinate. As above 

 stated, this method is amply borne out, and shown to be a natural 

 one, by the study of the development of leaves in the lower vascular 

 plants. 



The second part of the paper is devoted to a detailed comparison 



