Podostemacece. 1 7 1 



oblong shape, with an hour-glass construction in the middle. 

 This was first noticed by Griffith in his two species, and I 

 find that it also exists in my seven new ones, and in the one 

 from North America ; but it does not exist in the species of 

 Marathrum, nor in the two of Tristicha, which I describe in 

 this paper. 



Mniopsis of Martius is nearly allied to Podostemon, being 

 principally distinguished by its peculiar habit, a tooth that 

 exists in the fork of the united filaments, which is probably 

 the rudiment of a fifth filament, and by its smooth, not 

 ribbed, capsule. 



Tristicha of Thouars, a musciform cosmolite genus, is 

 perhaps the most interesting of the whole group, as the more 

 perfect structure of its flowers leads to important conclu- 

 sions, with regard to the natural affinities of the tribe. It is 

 well characterized by its true perigonium of 3 imbricated 

 segments, 1-3-stamens, all of which are fertile, and 3-celled 

 ovary. 



The two remaining genera Hydrostachys and Halophila, 

 of Thouars, are natives of Madagascar, the Red Sea, and 

 the Ladrone Islands, with opposite, stipulate ? leaves, and 

 plantago-like spikes of flowers, the structure of which are 

 not so well known as those of the other genera. 



But little, that is satisfactory, has yet been pointed out 

 with regard to the affinities of these plants, notwithstanding 

 that some of the most eminent Botanists of the age have 

 written on the subject. Kunth, Richard, Martius, Bartling, 

 Arnott, and Bongard, consider the mass of their relation- 

 ships to be with monocotyledons. It is curious that al- 

 though Bongard held this opinion, he was the first to show 

 that the embryo is truly dicotyledonous. This fact has been 

 confirmed by Griffith, and I have myself determined such 

 to be the case in two species from Brazil, and in four others, 

 which are natives of India. The seeds are exalbuminous, 

 and the radical is inferior and directed towards the hilum. 



