DORS1VENTRAL SHOOTS. ANISOPHYLLY IN SPERMAPHYTA 109 



have larger axillary shoots than the smaller ones. The advantage of 

 the whole arrangement is evident the stronger development of the 

 leaves of the under side brings the assimilating leaf-surface more to 

 the periphery of the crown of the tree where the illumination is more 

 favourable J . 



b. HABITUAL ANISOPHYLLY. 



The cases to be mentioned here, and only a few can be referred to, 

 link on to that of Selaginella described above (p. 105). 



i. Urticaceae 2 . Fig. 62 is a representation of a portion of a 

 shoot of Pellionia Daveauana, and a number of species of Elatostemma 



FlG. 6-'. Pellionia Daveauana. Portion of a shoot with asymmetric leaves, a. the stipules of arrested leaves 

 which stand upon the upper side. The axillary stipule of the foliage-leaf stands more towards the under side, 

 and the whole appearance is as if each leaf had two stipules. 



exhibit features of a like kind. The shoot has apparently two rows 

 of leaves, but there are really four rows, the leaves being in decussate 

 pairs. The opposite leaves in each pair are very unequal in size and 



1 See the quotation from Herbert Spencer on page 99. Wiesner has termed ' the furtherance of 

 growth of the outer over the inner member of a lateral organ ' exotrophy ; see his Mittheilung iiber 

 die Erscheinung der Exotrophie, in Ber. der deutsch. bot. Ges. x (1892), p. 552. 



2 See Weddell, Monographic des Urticacees, in Arch, du Museum d'histoire nat. ix (1856). 



