BOT.— Vol. I.] CAMPBELL— NAIAS AND ZAMNICHELLIA. 7 



The genus Naias is of world-wide distribution, but owing 

 to the great simphcity of the flowers and the variation in 

 the habit of the same species, the limits of the species are 

 very uncertain. There are probably about ten species 

 known (Watson, 1880, p. 191; Morong, 1893, p, 60), of 

 which four occur in the United States, two of these being 

 found in California, (Watson, 1. c); i. e., N. Jlexilis 

 and N. major {N. marina L.). They are all entirely 

 submersed aquatics and remarkable for the extraordinary 

 simplicity of the flowers, which consist respectively of a 

 single carpel or stamen; and these are remarkably simple 

 in structure and curiously similar both in their origin 

 and early stages of development. It is generally con- 

 sidered that this extreme simplicity of structure is the result 

 of the aquatic environment, but this is by no means 

 certain, as the flowers cannot readily be considered as 

 derived from any more perfect type, and the genus stands 

 very much isolated. 



Magnus (1870) has given a very complete and accurate 

 account of the relation of the stem and leaves, and the posi- 

 tion of the flowers. The slender stem has the leaves 

 apparently in whorls of three, but a careful examination 

 shows that in reality one of these three leaves is the basal 

 leaf of a branch springing from the axil of one of the leaves. 

 Except for this basal leaf on each branch, the leaves are in 

 pairs, the lower of each pair always developing a branch from 

 its axil, while the upper one is invariably sterile. A further 

 examination shows that in place of the absent leaf at the 

 base of the branch there is a flower, which may be either 

 male or female in N. flexilis, but in N. major, which is 

 dioecious, is always of the same kind on one plant. These 

 flowers, as Magnus (1. c.) showed conclusively and as we 

 shall see later, are morphologically the equivalents of axes, 

 and the ovule and anther strictly terminal organs. Owing 

 to this formation of a branch in the axil of one of each pair of 

 leaves, the whole plant is bushy in form. Perhaps the most 

 remarkable thing in regard to the flowers is their striking simi- 

 larity, both in origin and structure, the male and female 



(2) June I, 1897. 



