OP CEYLON AND INDIA. 
431 
couple of South American forms. It is very greatly to be 
desired that the other Podostemaceæ should be studied in 
this respect. 
In plants which when mature show very unusual features 
in their morphological construction, such as the Cacti, 
Utricularias, &c., we are accustomed to derive valuable 
evidence as to the morphology of the plant from a study of 
its seedling, and the descriptions above given of the 
seedlings of many Podostemaceæ show that the seedling is 
a valuable subject for study here also, throwing considerable 
light on the morphology and the phylogeny of the thalli. 
Most of the interesting features of the seedlings have already 
been dealt with above under other heads, e.g.^ the progressive 
reduction of the primary axis, the development of the 
thallus, the lack of exact homology between the primary 
axis and the secondaries, and so on. Dorsiventrality does 
not appear in the seedlings except in one or two cases, e.^., 
in Podostemon to a very slight (and doubtfully hereditary) 
degree, and in Farmeria, in which as we have already seen 
the flower and fruit are extremely dorsiventral. The very 
peculiar case of the seedling of Lawia, in which dorsiven- 
trality is acquired soon after germination, deserves special 
mention. In the other seedlings complete dorsiventrality 
is not as a rule acquired, the primary axis remaining radial 
in symmetry, and the dorsiventrality showing in the thallus. 
Like the mature plants, the seedlings of the Ceylon forms 
have simple leaves, while the American forms mostly 
appear to have compound leaves appearing at once after the 
cotyledons. It would be interesting to know the reason of 
this difference. 
The seedling plants are well adapted to their peculiar 
conditions of germination and life. Except in Farmeria the 
seed is very small, and the seedling also, so that it is less 
liable to be carried away by the water, Haptera and 
rhizoids are formed at once on germination, so that the 
plant is firmly anchored, and as soon as possible the develop- 
ment of the thallus begins. In Farmeria metzgerioides, we 
