268 WILLIS : MORPHOLOGY OF THE PODOSTBMACEÆ 
the general life-history are unknown even for the compara- 
tively accessible forms, such as Podostemon Ceratophyllum, 
and the systematic position of the order is a matter of great 
differences of opinion, some writers putting it in one, some 
in another place ; e.g.^ near to the Saxifragaceæ, Caryophyl- 
laceæ, Lenti bo lariaceæ, Pistiaceæ, Lacistemaceæ, Elatinaceæ, 
Nepenthaceæ, Sarraceniaceæ, Piperaceæ, and elsewhere. 
The present paper is an attempt to clear up some of the 
darkness surrounding our knowledge of this order, so far as 
the Asiatic species are concerned. No one can be more 
conscious than myself of the defects and gaps in the work, 
but I hope that its publication may stimulate botanists who 
have the opportunity to study these plants in their natural 
habitats, where alone they can be properly dealt with. 
As to many botanical students the order is nothing but a 
name, it may be well at starting to mention that it consists 
entirely of submerged water plants, living only in rapids 
and waterfalls, firmly attached to the rocks on which they 
grow ; that their vegetative organs frequently consist very 
largely of thalli, which are very often of (phylogenetic) 
root ” nature ; and that both in external form and internal 
structure they simulate in the most remarkable way Algæ 
(e.g.^ Fucus), liverworts, mosses, and lichens. A glance at 
the plates at the end of this paper will show this. 
My observations have as yet been almost entirely confined 
to the Indian and Ceylonese species. By no means one of 
the least troublesome parts of the work has been the purely 
taxonomic labour of determining the limits of the genera 
and species, which have hitherto been very inaccurately 
defined. This work is as yet very incomplete, but so far as 
possible I have worked out the Indian and Ceylon forms, 
and the somewhat sweeping changes in the nomenclature 
and taxonomy which I have found necessary have been 
described in a preceding paper with the view of clearing 
the ground for the present work.^ As there explained, I first 
* Willis, A Revision of the Podostemaceæ of India and Ceylon, Ann. 
Perad. I., 1902, p. 181. 
