20 Alga'. 



many intermediate stages with species of Kiitzing's genus Glceotila, 

 and even with species of the genus Ulothrix. This was first 

 definitely shown by Gay 1 and afterwards emphasized by Klercker 2 . 

 But, although in some instances this is the case, and various 

 genera of the group ' Protococcoideae ' have to be transferred to 

 other groups to which they more rightly belong, many forms still 

 have to remain in the old group ' Protococcoidese ' until more is 

 known concerning their life-histories and affinities. For instance, 

 it has been asserted that species of the genus Tetraedron Kiitz. 

 1845 (= Polyedrium Nag. 1849) are merely stages in the develop- 

 ment of Pediastrum, but this is now known to be erroneous 3 , 

 and that even if certain forms are developed in the life-cycle of 

 Pediastrum which much resemble species of Tetraedron, yet the 

 latter genus is quite distinct and has a life-history of its own. It 

 is, however, most probable that Pediastrum has been evolved from 

 Algae of the nature of Tetraedron, and one of the connecting links 

 has been discovered in a genus recently described by Lagerheim 

 under the name of Euastropsis. 



As another example of erroneous conclusions arrived at from 

 insufficient evidence, there is the case of the genus Chantransia. 

 The discovery by Sirodot 4 of the ' protonema-stage ' of Batracho- 

 spermum was regarded by many people as a sufficient proof that 

 species of Chantransia were merely asexual forms of Batracho- 

 spermum. This was entirely due to the mistake of confounding 

 the sporophytic shoots of Batrachospermum (and Lemanea) with 

 certain true species of Chantransia which they much resembled. 

 Murray 5 , in commenting upon this, says that to speak of the 

 " Chantransia-forms " of these genera " means no more than if the 

 protonema of a moss were to be called its ' Conferva-farm ' or 

 the prothallus of a fern its ' Liverwort- form.' These growths of 

 Lemanea and Batrachospermum have nothing to do with the valid 

 generic type Chantransia" 



In conclusion, it seems well established that the higher types 

 of Algae have originated by gradual evolution from the more lowly 



1 Gay, ' Recherches sur le developpernent et la classification de qnelques Algues 

 Vertes,' Paris, 1891. 



2 Klercker, ' Ueber zwei Wasserformen von Stichococcus,' Flora, 1896. 



3 Cfr Lagerheim in Tromso Museums Aarshefter, 17. 1894. 



4 Sirodot, ' Sur le developpernent des Algues d'eau douce du genre Batracho- 

 spermum, ' Paris, 1875. 



5 G. Murray, ' An Introduction to the Study of Seaweeds,' London, 1895, p. 208. 



