Cfdorophyceeb 51 



presence of a pigment termed by Lagerheim phycoporphyriri 1 . 

 This violet colour occurs normally in Ancylonema Nordenskioldii 

 Berggr., Mesotwnium violascens De Bary, M. purpureum W. & 

 G. S. West and Mougeotia capucina (Bory) Ag., and under excep- 

 tional circumstances it is found in various species of Zygnema, 

 Spirogyra and Desmids. The Volvocacege and the zoogonidia and 

 gametes of other green Alga- 1 possess vibratile cilia, which are very 

 variable in their length, number, disposition, and symmetry; and 

 in certain of the same forms contractile vacuoles are present. In 

 the genera Tetraspora and Apiocystis ' pseudocilia ' are found, 

 which do not possess any power of movement. 



A single nucleus is present in the cells of all the green Algae 

 except the coenocytic and incompletely septate forms, and during 

 the formation of asexual non-motile spores, zoogonidia, or gametes, 

 it undergoes divisions corresponding to the divisions of the proto- 

 plasm. In some green Alga? mitotic division of a more or less 

 complex character has been observed-. 



The cell-wall is very variable and its structure is often difficult 

 of observation. In the formation of a cell-wall such as after the 

 quiescence of a zoogonidium, it is developed on the outer surface 

 of the protoplasm as the result of more or less complex processes. 

 The young cell- wall usually consists of cellulose, but sometimes 

 equally of pectose. Under the action of strong acids or other 

 hydrating reagents an ordinary thick cell-wall will swell up and 

 show traces of lamination. Each lamina represents successive 

 layers of growth in thickness and in most plants consists of a 

 mixture of cellulose and pectose constituents in variable propor- 

 tions. In the Chlorophycese these two constituents of the cell- 

 wall are differentiated while the wall is very young. They exhibit 

 considerable differences in their behaviour with reagents, the 

 cellulose constituents giving a violet colour with chlor-zinc-iodine 

 (Schulze's solution), whereas the pectose constituents do not. In 

 many Algse the pectose constituents of the cell-wall are in the 

 form of gelatinous layers on the outside of inner layers of cellulose. 

 This mucilaginous material stains readily with aniline dyes such 



1 Lagerheim in Videosk.-Selsk. Skrift., I niatbem.-uatur. Kl., Kristiania, 1895, 

 no. 5. 



2 Observed in Spirogyra by Mit/kewitsch (Flora, Ixxxv, 1898) and C. van 

 Wisselinsh (Bot. Zeitung, Ivi, 1898; Flora, Ixxxvii, 1900); in Chlamydowonn* by 

 Dangeard (Le Botaniste, vi, 1899) ; in Closterium by Klebahn ; also in llotry- 

 diurn, etc., etc. 



42 



