44 



BOTANY 



shoots of the same name these are elongated and enable the 

 bud produced at the end to develop at a distance from the parent 

 plant. Camptosorus rhizophyllns, an American Fern, is commonly 

 known as the Walking Fern. Such leaf-runners usually lose their 

 pinnae and are reduced to the leaf stalk. A particularly striking 

 appearance is presented in those cases in which the first leaf of the 

 bud in its turn forms a leaf-runner, so that a sympodium of runners 

 results (Asplenium obtusifolium, A. Mannii). 



A metamorphosis of the whole leaf lamina, or a part of it, into 

 tendrils (LEAF-TENDRILS) is of comparatively frequent occurrence, 



Kic. 17. l'tricu!<iriii~>-u.l<jari*. A, 1'art of leaf with several bladders (x 2). 11, Single pinnule of 

 leaf with bladder (x 6). C (after GOEBEL), Longitudinal section of a bladder (x 28) ; . valve ; 

 ", wall of bladder. 



especially among the Papilionaceae. In the leaf of the Pea (Fig. 48), 

 the leaflets of the upper pairs have become transformed into delicate 

 tendrils which have the power of twining about a support. In the 

 case of the yellow Vetchling, Lathyrus Apliaca (Fig. 49), the whole 

 leaf is reduced to a tendril and the function of the leaf -blade is 

 assumed by the stipules (ri). A comparison between these two forms 

 is phylogenetically instructive, as it indicates the steps of the gradu- 

 ally modifying processes which have resulted in the complete reduction 

 of the leaf lamina of Lathyrus. The comparison of the two preced- 

 ing cases with Ampelopsis (Fig. 29) will make the distinction between 

 these tendrils and stem-tendrils clear, and indicate the value of 

 comparative morphological investigation. 



In Lathyrus Aphaca the stipules assume the function of the meta- 



