196 RECENT LITERATURE ON FRESHWATER ALGxE. 



short ") D. Zanzibar ieusis. Authentic specimens of both these 

 plants are in the British Museum Herbarium, and though it is 

 plain that D. amhoinensis and D. Zanzibar iensis are two distinct 

 species, the difference between D. zanzibariensis and Caloglossa 

 Leprieurii is not so obvious. 



The British Museum has a large series of specimens of the 

 latter plant from many parts of the world : the North and South 

 Atlantic (New York, New Jersey, Florida, Guadeloupe, Cayenne), 

 Cape of Good Hope, Australia, Tasmania, New Zealand, and the 

 Indian Ocean (Mauritms, freshwater and marine, Ceylon, and 

 Calcutta), these including, of course, both marine and freshwater 

 records. The Ceylon specimens are described by Prof. Cramer in 

 his exhaustive paper on C. Lrprienrii (S. A. aus der Festschrift 

 z. Feier d. 50-jahrig. Doctorjub. von Nageli u. Kolliker, Ziirich, 

 1891). Comparison between these Indian Ocean specimens and 

 D. zanzibariensis point very strongly to the fact of their being one 

 and the sauie species. The position of the tetraspores in the two 

 plants might at first sight seem to argue a possible specific differ- 

 ence, since in C. Leprieurii they grow in lines radiating outwards 

 and upwards from the midrib, the number of sporangia in such 

 lines varying with the width of the plant ; while in D. zanzibariensis 

 they are described as occurring in one or two rows along the mid- 

 rib. But the thallus of D. zanzibariensis is as a rule narrower than 

 the usual form of C. Leprieurii, and the space between the midrib 

 and the edge of the thallus is too limited to allow the growth of 

 more than one or two rows of sporangia. 



C. Leprieurii is shown by Prof. Cramer (/. c.) to be a very 

 variable plant in respect of size and breadth of the thallus, and it 

 would be difficult, perhaps impossible, to show in what way D. zan- 

 zibariensis can be considered specifically distinct from C. Leprieurii. 

 It is clear therefore that Prof. Goebel ought to reconsider the pro- 

 priety of maintaining his "new species." 



If it be granted that these two plants belong to the same 

 species, the question of geographical distribution put forward by 

 Prof. Goebel is more easily solved than is otherwise possible. He 

 asks with solemnity what has become of the common marine 

 ancestor of D, zanzibariensis and D. amhoinensis, both found on 

 islands separated by the whole width of the Indian Ocean ? Is 

 this ancestor still living, or has it died out, leaving only freshwater 

 descendants ? Now, allowing D. zanzibariensis to be but a form of 

 Caloglossa Leprieurii, the answer is obvious. Caloglossa occurs 

 throughout the Indian Ocean as a marine and brackish water 

 plant ; in Mauritius, indeed, it grows inland in a mountain stream. 

 What more likely than that a form of this variable plant has 

 become modified to its surroundings in Amboyna, and is regarded 

 as the Delesseria auiboinensis of Karsten ? 



The finding of the fruit of D. amboinensis will help to deter- 

 mine its true position, but in any case there is a near relationship 

 between it and C. Leprieurii ; and if, as is suggested by Mr. Karsteii, 

 the Amboyna alga, once marine, has accommodated itself to 

 changed conditions consequent on a gradual raising of its habitat 



