30 



PART I. THE MORPHOLOGY OF PLANTS. 



[4. 



in Selaginella, likewise, the leaves are borne on the dorsal and 

 ventral surfaces, and the branches on the flanks. In Utricularia, 

 and in the inflorescences of the Boraginacese, the branches are 

 borne on the dorsal surface, the leaves (when present) on the 

 flanks. In the Lemnaceae, the branches are produced on the dor- 

 sal, the roots on the ventral, side of the shoot. 



The members borne on the flanks, in these cases, are in rows, one 

 on each flank ; and a similar serial arrangement can usually be 

 traced in the members borne on the dorsal and ventral surfaces. 

 Thus, in the inflorescences of the Boraginacese, tbe flowers are ar- 

 ranged in two longitudinal rows ; in those of the Vetches there 

 may be two rows (Vicia Faba, commonly), or many rows (Vicia 

 Cracca). The leaves of some Algae such as Caulerpa (Fig. 17) and 



Fig. 17. A portion of the body of Caulerpa plumaris showing dorsiventral arrangement 

 of members. The horizontal stem bears leaves on its upper (dorsal) surface, and roots on its 

 lower (ventral) surface. 



Herposiphonia (Fig. 3) are borne in one row on the dorsal, and 

 the roots in one row on the ventral surface of the stem ; similarly 

 in some Ferns (Lygodium palmatum, Polypodlum Heracleum) there 

 is a single dorsal row of leaves. In Azolla, Pilularia, and Marsilea, 

 there are two dorsal row of leaves, in Selaginella there are two 

 ventral and two dorsal rows of leaves, and in Salvinia two ventral 

 and four dorsal rows. 



The whorled arrangement is not excluded by dorsiventrality : 

 for instance, in Salvinia, the leaves are arranged in alternating 

 whorls of three, two of the leaves being borne dorsally, and the 

 third ventrally, and thus the four dorsal and the two ventral rows 

 of leaves are produced. 



