300 



NOTES ON BRITISH DESMIDIE^. 



pa^Der, not only did the species named remain true to their respec- 

 tive t)rpes, but even the intermediate species fell in between them 

 in an order that, within certain limits, was more uniform than 

 could have been expected. Now if good specimens of the four 

 species named be selected and compared with one another, it w^ill 

 be seen that they exhibit a well-marked gradation of forms, which 

 pass from the almost true dichasium of G. prateme to the cicinal 

 cyme of G. molle. Moreover, if, as may easily be done, the 

 remaining British species be intercalated between these, we shall 

 have a complete view of of the successive steps by which the 

 transition has been effected. 



It is unnecessary to give illustrations of all the species, but the 

 appended diagrammatic figures of the four typical forms (Figs. 3, 

 4, 5, 6) may help to give clearness to what has been said. 



Explanation of Figures. 



Fig. 1. Empirical diagrammatic view of G. Bohertianum. 



2. Rational do. do. 



3. Rational do. G. pratense. 



4. Rational do. G. Robertianum. 



5. Rational do. G. columbinum. 



6. Rational do. G. molle. 



NOTES ON BKITISH DESMIDIE^. 



By W. Joshua, F.L.S. 



The following species have this year come under my own 

 observation more or less abundantly in a state of conjugation 

 with their zygospores, among Alg^e collected in various parts of the 

 British Islands. The occurence of zygospores in so many sx3ecies, 

 considerably above the number recorded by Ralfs, and in some but 

 very rarely found in that state of development, is possibly 

 attributable to the high condition of temperature during the winter 

 and early spring months. One species, Fenium phi/matosponwi, 

 has not been previously recorded as British. 



