OF CEYLON AND INDIA. 
437 
the larger upper valve persisting, while the smaller lower 
one falls off. 
In Griffithella the vegetative organs are like those of 
Dicræa, but the secondary shoots appear to be more prostrate 
at an early period ; the question, however, requires further 
investigation. The flower and fruit show similar zygomor- 
phism to that of Podostemon. The same is the case in 
Willisia, though the secondary shoots at the flowering time 
are stiffly erect ; their condition in the earlier period of the 
life-history has yet to be discovered. The thallus of this 
species, at any rate, is highly dorsiventral. In Castelnavia 
there is a highly dorsiventral thallus, accompanied by 
extreme zygomorphism of the flower and fruit ; in some 
species the flowers are developed in a horizontal position 
in cavities of the thallus. 
In Hydrobryum the thallus is also highly dorsiventral ; 
the secondary shoots are like those of Dicræa, and late in life 
as the flowers develop, become exceedingly dorsiventral in 
structure, showing it in a high degree in the bracts, and in 
the spathe, which splits along the upper side. The flower, 
though developed in a more or less prostrate position, 
stands erect as soon as it emerges from the spathe, at least 
in those forms in which it possesses a stalk, while in the 
stalkless forms the ovary and stamens curve upwards as 
much as possible. It is extremely zygomorphic, and the 
various species show different degrees of the phenomenon. 
All show it in the stamens, but in H. Griffithii the fruit is 
only very slightly zygomorphic, though as it ripens it 
becomes more or less prostrate ; in H. sessile it is aniso- 
lobous and erect, and in H. olivaceum much the same, while 
in H. lichenoides its zygomorphism is extreme, correlated 
perhaps with the fact that in this form the secondary shoots 
are often comparatively prostrate throughout their life. In 
Farmeria the morphological construction is similar to that 
in H. lichenoides, and here we find the most extreme dorsi- 
ventrality in the family, though the flower still curves 
upwards when the spathe splits. The lower loculus of the 
