Adaptation in the Tristichacece and Podostemacece. 539 



ventrality than do half of the Tristichacese. They have creeping roots which 

 give rise to secondary dorsi ventral shoots with large leaves developed in two 

 ranks. The flowers are radially symmetrical, but are liable at times to become 

 slightly dorsiventral by the abortion of some of the stamens. The inflorescence 

 in Mourera is flat. 



A further stage in this direction is shown in the South American 

 Lophogynes and Apinagias, where the secondary shoots, while smaller in 

 size, have become more or less flattened out and thalloid by the union of the 

 bases of the leaves or the flattening of the stem. The flowers are usually 

 markedly dorsiventral by the disappearance of the upper stamens. An 

 extreme case of this construction is afforded by Castelnavia, where the 

 (secondary) thalloid shoots He flat upon the rock, like the (primary) shoots of 

 Lawia in the other order. 



Another section of the family is represented by the Podostemons ; 

 occurring in Asia and America, and probably in Africa also, where the root 

 is more or less cylindrical and creeping, and gives rise to secondary shoots 

 which are only slightly dorsiventral, chiefly in their branching, and which 

 bear highly dorsiventral flowers. Allied to this genus, as well as perhaps to 

 Lophogyne, etc., is Mniopsis, which is confined to South America, has 

 a thallus like Lophogyne, and a flower like Podostemon. 



Spluerothylax abyssinica Warming (Abyssinia) has what is apparently 

 a primary axis that grows up to a considerable height, bearing compound 

 leaves and flowers, while at the same time the root at the base forms a flat 

 thallus, something like a lichen or a liverwort, bearing secondary shoots 

 which remain very short, and ultimately become floriferous also. The 

 flowers are highly dorsiventral. In H. olivaceum and other species of 

 Hydrobryurn (India and Ceylon) the primary axis is much reduced, only 

 seldom bearing flowers, but the flat lichen-like thallus or root is large, and 

 gives rise to great numbers of secondary shoots, which ultimately become 

 floriferous, with very markedly dorsiventral flowers. 



In Dicrsea and Griffithella the root flattens out, sometimes in long thread- 

 or ribbon-like forms, sometimes in more condensed shape, sometimes even 

 forming a goblet-like organ. On the edges are borne the secondary shoots, 

 which are very short, lengthening slightly at the end of the season, when 

 they bear each a dorsiventral flower. 



In Farmeria (India, Ceylon) the roots are creeping and flattened, as in 

 Hydrobryurn, but the flower carries the dorsiventrality to the last stage, 

 showing it in the interior of the ovary, and in the embryo. In one species, 

 F. metzgerioides Willis, the fruit contains only two seeds, and does not 

 dehisce, the seeds germinating in situ on the rock. This is the only species 



