26 A Igce 



as SticJiococcus, Hormospora, Radio/Hum, Gloeotila and Geminella, 

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

 bedded in a gelatinous envelope. 



The Chaatophoracea? are further specialized forms of the Ulo- 

 trichacese, which are distinguished mainly by their branched habit. 

 The polymorphism exhibited by the Chjetophoracese, and the deve- 

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

 a close connection with the Palmellacese, but probably through the 

 Ulotrichacese. Chodat considers the genus Pleurococcus as one type 

 of the Chaetophoracese 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 Ulvacese, especially such forms as Monostroma 

 and Ulva, have most likely originated from Palmellaceous Alga? 

 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 Alga?. It may have originated from some aber- 

 rant form of the Ulotrichacea?, 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 

 Cladophoracese (and therefore the Pithophoracese) may thus have 

 had an origin from the Microsporacea?. Bohlin 1 has recently 

 transferred the Cladophoracese to the order Siphonea? owing to 

 the coenocytic 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- 

 phoracese. Since 1897- I have regarded the Cladophoracese as a 

 distinct family of Chlorophyceae, in close proximity to the Siphoneae 

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

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

 place the Cladophoracese and Pithophoracese, along with the 

 Sphseropleacese, in a separate order, the Cladophorales. 



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

 Afhandl. Upsala, 1901. 



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



