The Morphology of Ruppia Maritima. 73 



Irmisch ( J858j investigated the vegetative branching of Zannichelha 

 and found it to be a pure sympodium as regards its horizontal axis. 

 This develops beyond its second leaf into an upright shoot, which 

 ultimately bears the flowers ; at its base, however, from the axil of 

 the second leaf, arises a branch which prolongs the horizontal axis. 

 This again, after two leaves are given oif, develops into an upright 

 shoot and the horizontal axis is again repeated from a branch in 

 the axil of the second leaf. This process goes on indefinitely, so 

 that the horizontal axis is therefore merely a succession of generations 

 of axillary branches and hence a pure sympodium. 



The branching of Naias is peculiar, according to Campbell's (1897) 

 interpretation. The leaves are developed approximately in pairs — 

 one slightly below the other and larger. From the axil of this 

 lower one a primordium arises which by dichotomy produces a 

 flower and a lateral branch. The branch bears at its base a single 

 leaf. The upper leaf of the original pair is sterile, so that the stem 

 of Naias has its leaves apparently in whorls of three, with a branch 

 and flower arising from each whorl. Apparently the apex of the 

 main stem never terminates its growth, but goes on producing its 

 pairs of leaves — one sterile and one fertile — so that the system is 

 very unlike that of Ruppia. 



Cymodocea, an entirely submerged marine genus, distinguished 

 by its long ribbon-like leaves, very simple flowers and filamentous 

 pollen, is placed by Ascherson (1889) next in order to Ruppia. 

 In Cymodocea nodosa, Bornet (1864, pp. 15 ff.) describes types of 

 branching which conform to those of Ruppia. The vegetative 

 branching is monopodial, and a longitudinal section of the bud 

 (1. c. PL IV, fig. 1) resembles very closely that of Ruppia. The 

 flowers are terminal and the growth in length is continued by a 

 lateral bud. It appears, however, that this bud is not necessarily 

 one of the two buds nearest the flower. 



In Zostera the rootstock is also monopodial, the inflorescent 

 system being sympodial (Sauvageau, 1891, I). 



Phyllospadix closely resembles Zostera (Dudley, 1893). 



In Althenia (Prillieux, 1864), on the other hand, a genus resem- 

 bling Zannichellia and found in Europe, Africa and Australia, the 

 vegetative branching is sympodial, much as in Zannichellia. The 

 growth of the rootstock is continued by successive branches from 

 the horizontal axis which in each case itself becomes vertical and 

 bears the flowers. The flowers are unisexual — the male terminating 

 the upright axis or stem. In the axils of the two leaves subtending 

 the male flower arise secondary branches, which bear male or 



