46 



Veit Brecher Wittrock. 



and so on. What has now been said may suffice to show that the 

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

 of a more subordinate kind. 



VII. ON THE GEOGRAPHICAL DISTRIBUTION. 



The Pithophoracece, being algai, are principally aquatic plants. 

 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 land, 

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

 (v. Mart.) 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 P'rthophoracece 

 grow only in fresh water. Not 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. keicensis 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. cequalis nob., P. oedogonia (Mont.) nob., P. Cleveana 

 nob., P. polymorpha nob. and P. Roettleri (Roth) nob.; P. Zelleri (v. 

 Mart.) nob. belongs to a subtropical climate. That P. keicensis 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 

 Waterlily-house belonging to the Botanical Garden at Kew. The species 

 here grows together with tropical Nymphceacece 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 

 aquaria at Kew, nor in the ponds and small lakes belonging to the 

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

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

 with the rhizomes of the JSfymphwacece 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- 

 minated and brought forth specimens of the Pithophora capable of pro- 

 pagation. If we suppose P. ke-wensis nob. also to have a tropical origin, 



