426 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
dorsiventrality of structure of these organs which accom- 
panies the increasing prostrateness of the shoot. In the 
comparatively erect shoots the bracts are only slightly thicker 
on the upper than on the lower side, and the spathe stands 
erect and splits fairly uniformly into teeth at the tip, while 
in the Hydrobryums, &c., the bracts are very prostrate and 
much thicker on the upper side, and the spathe lies prostrate, 
splitting on the upper side to let the flower escape. In 
Lawia the spathe is physiologically represented by the 
cupule, which shows a marked dorsiventrality similar to that 
of the vegetative growing apices, and varying in the different 
forms. 
Another interesting feature about these organs is the 
deciduous cortex of the pedicel, a phenomenon common 
to all the Indian and probably most or all of the other 
species. The length of the pedicel, as pointed out in the 
preceding paper, is a very variable feature, and the causes 
determining it require investigation. 
The Flower and Fruit. 
The main features of the morphology of these organs have 
been considered from a taxonomic point of view in the 
previous paper (p. 194), and need not be repeated here. 
Detailed accounts of many flowers and fruits may be found 
in the works of Tulasne and Warming, and also in the 
present paper. 
The most interesting general features of the floral morpho- 
logy are the substitution of the spathe for the perianth in 
all the more modified tribes, and the progressive dorsiven- 
trality of the flower, which will be considered below. This 
dorsiventrality at last shows in the fruit also, the lower 
loculus being reduced or even abortive, and the ripe fruit 
splitting obliquely into tAvo unequal valves. The develop- 
ment or absence of ribs in the wall of the ripe fruit is a 
character of anatomical and taxonomic importance. It has 
been sufficiently described and figured above under Dicræa, 
