On the Leaf Scars of Lepiclodendron. 79 



gin. When the scars are connected by merely the extension 

 of the keeled medial line, two margins are at intervals 

 brought side by side, so that each leaf scar has double mar- 

 gins upon two opposite sides, if we regard the scar as a quad- 

 rilateral. Or to state the fact differently, in one oblique di- 

 rection or spiral, the leaf scars are separated by double mar- 

 gins, produced by bringing scars adjacent which are members 

 of alternate series. The expansion or increase in circumfer- 

 ence of the cortex is effected by widening and consequent 

 cracking of the margins.. The direction of the fissures is 

 usually obliquely across the margins, in consequence of being 

 necessarily the resultant of the lines perpendicular to the di- 

 rections of expansion, together with the flexuosity of the mar- 

 gins. It cannot be maintained that the margins, in the speci- 

 mens furnishing the figures above referred to, are in any im- 

 portant degree produced by the widening of the cortex after 

 the leaves attained their full size ; because in that case, on ac- 

 count of the direction of the cracks, the fine keeled lines con- 

 necting the elevated leaf bases would be broken and ob- 

 literated by fissures extending across the double margins. 

 This partly accounts for the rarity of the feature. Conse- 

 quently we may affirm that this form is the natural typical 

 relation of the leaf scars of this species, assumed when the 

 leaves are not crowded, but have sufficient space upon the 

 stem for their normal development. The proportions of the 

 leaf scars vary, without obliteration or change of any charac- 

 ter, from obovate to narrow elliptical, or the length from two 

 to five times the breadth, not including the extension of the 

 medial line. The extreme forms I have not figured. Any ob 

 liquify will, of course, make them rhombic or rhomboidal, 

 which is slightly the condition in Figs. 1, 2, PI. Y, and more 

 so in Fig. 5, PI. YI. But if the leaf scars are somewhat 

 obovate, the obliquity will make their trapeziform shape more 

 prominent. These variations in shape are greater in the de- 

 rived forms, which will be considered hereafter. Although 

 the exact shape of the general cicatrix is in many descriptions 

 made one of the distinctive characters of the particular 

 species, in L. aculeatum, at least, the shape even of the typical 



