34 



BOTANY 



only from the mode of their development but also from the possibility 

 of transforming them into foliage leaves. Goebel, by removing the 

 growing tip and foliage leaves of a shoot, succeeded in forcing it to 

 develop other foliage leaves from its scale leaves. Bhizomes, grown 

 in the light, develop foliage leaves in place of the usual scale leaves, 

 and even on a potato it is possible to induce the formation of small 

 foliage leaves instead of the customary scale leaves. 



Leaf-Sears. — After a leaf has fallen, its previous point of insertion 

 on the stem is marked by the cicatrix or scar left by the fallen leaf. 

 In winter, accordingly, when the trees are denuded of their leaves, the 

 axillary buds are plainly perceptible above the leaf-scars. 



The Metamorphosis of Foliage Leaves. — A form of slightly modi- 

 fied foliage leaves is seen 

 in peltate leaves, or those 

 of which the petioles are 

 attached to their lower 

 surfaces somewhat within 

 the margin, as in the leaves 

 of the Indian Cress (Tro- 

 pae-ohtrn inajus, Fig. 180). 

 In the process of their de- 

 velopment the young leaf- 

 blades, in this case, grow 

 not only in the same direc- 

 tion as the petioles, as a 

 prolongation of them, but 

 also horizontally in front 

 of them. The tubular leaves 

 of many insectivorous plants 

 may have commenced their 

 development in much the 

 same way. The leaves of 

 Nepenthes robitsta (Fig. 33), 

 for example, in the course 

 of adaptation to the per- 

 formance of their special 

 function, have acquired the 

 form of a pitcher with a 

 lid which is closed in 

 young leaves, but eventu- 

 ally opens. The pitcher, as 

 Goebel has shown, arises 

 as a modification of the leaf-blade. At the same time the leaf- 

 base becomes expanded into a leaf -like body, while the petiole 

 between the two parts sometimes fulfils the office of a tendril. By 

 a similar metamorphosis of its leaflets, bladder -like cavities are 



Fig. 33. — Nepenthes robusta. (^ nat. size.) 



