46 Veit Brixiier Wittrock. 



and so ou. Wliat has now becu said may suftice to show that the 

 dififerences in size within the group also give specific characters, though 

 of a more subordinate kind. 



VII. ON THE GEOGRAPHICAL DISTRIBUTION. 



The Flthophorac('(X'^ being algas, are principally a(|uatic jihuits. 

 Six of the species (eight in number) which are as yet known have 

 been found in water. One, P. Cleveana nob., has been found on laud, 

 viz. on humid earth in the shade of bushes. How it is with /*. Zelleri 

 (v. 3Iart.) nob. can not be decided with certainty from the information 

 which I have regarding it. It is said of this species, that it grows in 

 rice fields, but whether in water or on wet earth is not said. 



It has already been mentioned that the aquatic Pit]u>plwraccœ 

 grow only in fresh water. Xot one is known from wholly salt water, 

 and only of one, the australian sterile form existent in the Grunowian 

 collection, it is said that it occurs both in brackish and fresh water. 



With the exception of P. kewensk nob. all the species of this 

 order have been found in warmer climates. By far the greatest part 

 are even of a tropical origin. This is the case with P. sumatrana 

 (v. Mart.) nob., P. œqualk nob., P. oedogonia (Mont.) nob., P. Cleveana 

 nob., P. poli/inor/^ha nob. and P. Roettleii (Roth) nob.; P. Zelleri (v. 

 Mart.) nob. belongs to a subtropical climate. That P. kewensis nob., 

 which has been found in England, also draws its origin from warmer 

 countries, may be regarded as almost quite certain. This supposition 

 is powerfully supported by the nature of its locality, which is, as has 

 been mentioned in the introduction, the Tropical Aquarium or so-called 

 WaterlilyThouse belonging to the Botanical Garden at Kew. The species 

 here grows together with tropical NyinpJiœaceœ and other tropical aquatic 

 plants in water which is always kept at a comparatively high degree 

 of warmth. According to my researches it does not grow in the other 

 a([uaria at Kew, nor in the ponds and small lakes belonging to the 

 garden. With a very great probability, as it seems to me, we maj^ 

 therefore conclude that spores of P. keice7isis nob. have been brought 

 with the rhizomes of the JSFymphceaceœ or other aquatic plants from some 

 tropical country, and that they have afterwards, when they have found 

 circumstances advantageous to their development in the aquarium, ger- 

 mhiated and brought forth specimens of the Pitliopliora capable of pro- 

 pagation. If we suppose P. keicensis nob. also to have a tropical origin, 



