38 CALIFORNIA ACADEMY OF SCIEMCES. [Proc. 3D Ser. 



The general study of the apex of the stem and the origin 

 of the lateral members is very much as in JVaias. The 

 stem-apex shows a conical form, and from it are produced 

 the leaves in a quite similar manner. It differs from Naias 

 in the formation of the sheath (fig. 81, 5/^) below each node. 

 As in Naias, the lower of the two leaves alone develops 

 axillary structures, the upper one being sterile. The pro- 

 ducts developed from the axil of the lower leaf of the pair 

 are the stamen and a lateral branch. Schumann considers 

 that the apex of the main axis develops into the female in- 

 florescence and that the continuation of the axis, which is 

 a sympodium, is due to the development of a lateral shoot 

 in the axil of the second leaf. In reality the second leaf 

 does not develop any axillary structure at all, but the apex 

 of the stem divides into two equal parts, one of which de- 

 velops into the female inflorescence, while the other con- 

 tinues as the main axis of the stem, which is therefore not 

 such a sympodial structure as Schumann and Irmisch sup- 

 posed. The stamen bears precisely the same relation to 

 the lateral branches that the female inflorescence does to 

 the main axis; i. e., there is a division of the axillary prim- 

 ordium into equal parts, one of which becomes the stamen, 

 the other the lateral branch, which is, therefore, not to be 

 considered as an axillary structure arising from the basal leaf 

 of the staminal shoot. 



II. The Stem- Apex. 



The apex of the shoot is occupied by a more or less 

 conical growing point, whose tissues show the usual arrange- 

 ment, but the appearance varies a good deal, depending 

 upon the stage of development of the appendicular organs. 

 The general arrangement of the latter is well shown in fig. 

 83. At the base of the apical complex is the sheath (sh) 

 formed at the base of each node of the stem. Above this 

 are the two leaves (P and P), and in the axil of the lower 

 one is the primordium ( 5 ), which later gives rise to the 

 stamen and lateral branch. The prominence (x) at the 



