424 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
The Leaves» 
'These require but little discussion here. A distinction 
must of course be indicated between those of the primary 
and those of the secondary shoots, though in fact they appear 
to be quite similar in structure. In the Tristicheæ the leaves 
are singularly like those of many mosses, small, entire, and 
extremely delicate. In Mourera and other South American 
forms they are often of large or even immense size, and 
exhibit forms like those of many marine algæ. In the Indian 
Podostemeæ, however, they are always simple and usually 
subulate or linear. The two species of Podostemon, and 
Willisia selaginoides, have long leaves of considerable size, 
and those of Hydrobryum olivaceum may reach 10 cm. in 
length, but in the other forms the leaves are very small, 
rarely over 1 cm. long. 
The dimorphism of the apical leaves in Lawia is very 
interesting, and is parallelled by what is found in Selaginella, 
and analogous to the construction of some mosses or liver-, 
worts. A time-dimorphism occurs in nearly all the other 
genera found in India. The vegetative leaves, as already 
sufficiently described, have slightly sheathing bases, but 
while the flower is developing the bases of the leaves become 
much enlarged and form sheathing scaly bracts, while the 
tips fall away. These scales show a lateral dorsiventrality 
of structure, in that the sheath is thicker on the upper side, 
and the more so the more marked the dorsiventrality of the 
secondary shoot. 
A noteworthy feature of the leaves of the Indian Podos- 
temeæ is the development of hairs upon the upper side, 
presumably for enlarging the absorbing area, as with the 
“ Kiemenbüschel ” described by Goebel and Warming in 
many South American forms. 
The Hapfera. 
The morphology and the phylogeny of the peculiar 
anchorage organs which are so common in the order, and 
