Allgemeines. 1Q5 



shoot as in the other genera. The pedicel oi the erect flower is sur- 

 rounded by a horizontal or ascending cupule, which frequently remains 

 closed over the tip of the former until exposed to the air; the cupule is 

 dorsiventral in its structure. The flower itself is radial and resembles 

 that of Tristiclw in all essential points ; its radial symmetry is striking, 

 when compared with the very marked dorsiventrality of the vegeta- 

 tive parts. 



In Podostemon subulatus Gardn., the cotyledons are short and 

 subulate, but the earliest stages otherwise resemble those of the species 

 just described. The primary axis is only very slightly developed and 

 remains more or less erect, but the cotyledons and the few subsequently 

 formed leaves bend over tovvards one side. The thallus is developed 

 endogenously, emerging from the base of the hypocotyl, usually at right 

 angles to the plane of the cotyledons; its extreme tip is formed by a 

 non deciduons collenchymatous layer. Exogenous branches are soon 

 tormed and arise so near to the apex of the thallus, that, as in 

 Lauria, there is apparent dichotomy; of the two arms thus formed 

 one generali)- grows much more rapidly than the other, and since at 

 successive branchings this is repeated on alternate sides, the thallus 

 becomes more or less zig-zag in its construction. At each branching of 

 the thallus a somewhat dorsiventral secondary shoot is developed; this 

 bears distichous long, red leaves and is generally more or less erect, 

 attaining a height of as much as 3 cm. Subsequently branches, each 

 bearing a terminal flower, are developed from the lower axils of dithe- 

 cous leaves on the secondary schoots. The anemophilous flower is en- 

 closed in a spathe, which does not open until exposed to the air; the 

 perianth is wanting (or possibly represented by certain thread-like 

 organs) and the androecium is situated on the lower side, consisting of 

 two stamens with partially united filaments. The bilocular ovary has 

 numerous ovules and two Stigmas. In this and all the following genera 

 the outer tissue of the ovary falls away with the outer tissue of the 

 pedicel, leaving only the vascular tissues, which generally form ribs 

 on the fruit. In Podostemon the two lobes of the fruit are unequal and 

 one falls away, leaving the other on the stalk. — In the other species, 

 P. Barberi Willis, the thallus is somewhat flattened, the leaves are 

 smaller, and the flowers contain only a Single stamen and are cleisto- 

 gamous. In both species the thallus has a kind of continuous foot, 

 composed of root-hairs closely matted together, running along the middle 

 of the lower side. — Although the vegetative parts are less dorsiventral 

 than in Lanria, the flower is here strongly so. 



The genus Dicraea has very characteristic root-thalli and shows 

 considerable polymorphism in these organs. The germination resembles 

 that of the species already discussed The primary axis is quite 

 insigniiicant and the thallus appears almost at once, originating endo- 

 genously (possibly sometimes exogenously); the young seedling usually 

 has a distinct hapteron of exogenous origin. In D. elongata Jul., the 

 cylindrical thallus, after growing along the rock for a few millimetres, 

 forms an exogenous branch on its upper side, while its own growth 

 ceases. This branch develops into a long drifting thallus, attached to 

 the rock at its basal end only and provided with a small, terminal root- 

 cap ; such branches form the chief part of the mature plant and carry on 

 a large part of the work of assimilation. The thallus branches freely 

 upon or near to the rock, but only rarely in the drifting portions. 

 Endogenous secondary shoots are developed on the thalli in acropetal 

 succession, but only the small subulate leaves, wnich, as frequently 

 amongst the Podostemaceae, are hairy on the upper side, come above 

 the surface. As a rule about one-third or one-half of the entire number 

 of secondary shoots — situated on the basal portions of the thalli 

 become iloriierous, their axes appearing above the surface and each 

 bearing a Single flower. The vascular bundles, running to the flowering 

 shoots, now develop typical xylem-vessels and the inner collenchymatous 

 cortex of the thallus becomes very thick-walled in that region, whilst the 



13* 



