26 Algce 



as Stichococcus, Hormospora, Radiofilum, Glceotila and GemineUa t 

 forms in which simple loosely connected series of cells occur em- 

 bedded in a gelatinous envelope. 



The Chaetophoraceae are further specialized forms of the Ulo- 

 trichaceae, which are distinguished mainly by their branched habit. 

 The polymorphism exhibited by the Chaetophoracese, and the deve- 

 lopment of zoogonidia and formation of resting-spores, also indicate 

 a close connection with the Palmellaceae, but probably through the 

 Ulotrichaceafi. Chodat considers the genus Pleurococcus as one type 

 of the Chaetophoraceae which has been reduced owing to its existence 

 as a lichen-gonidium, but this is a statement I cannot agree with. 



The Ulvales and the Schizogoniales are parallel groups, each 

 of which has probably had a separate origin from the Proto- 

 coccoideae. The Ulvaceae, especially such forms as Monostroma 

 and Ulva, have most likely originated from Palmellaceous Algae 

 of the nature of Tetraspora. 



The genus Microspora is difficult to relegate to its proper 

 place in a classificatory scheme. It is the sole representative of 

 the family Microsporaceae and its characters mark it off sharply 

 from other green Algae. It may have originated from some aber- 

 rant form of the Ulotrichaceae, but its affinities are at present 

 doubtful. It is possible that the forms placed in the genus 

 Rhizoclonium have originated from Microspora, and by a further 

 specialization the genus Cladophora has been produced. The 

 Cladophoraceae (and therefore the Pithophoraceae) may thus have 

 had an origin from the Microsporacese. Bohlin 1 has recently 

 transferred the Cladophoraceae to the order Siphoneae owing to 

 the ccenocytic nature of the segments of the thallus, but the 

 validity of such a change is a question of opinion. Owing to the 

 many points of resemblance between Hydrodictyon and Cladophora,, 

 the former genus may possibly be a degenerate form of the Clado- 

 phoraceae. Since 1897 2 I have regarded the Cladophoraceae as a 

 distinct family of Chlorophyceae, in close proximity to the Siphoneae 

 and far removed from the Ulotrichacese, yet I hardly see the justi- 

 fication for its inclusion in the Siphoneae. I think it better to 

 place the Cladophoraceae and Pithophoraceae, along with the 

 Sphaeropleaceae, in a separate order, the Cladophorales. 



1 Bohlin, 'Utkast till de Grona Algernas och Arkegoniaternaa Fylogeni,' Akad. 

 Afhandl. Upsala, 1901. 



2 W. & G. S. West in Journ. Boy. Micr. Soc. 1897, p. 475. 



