Cilia and chloroplasts 



129 



mitotic to amitotic. Gerassimoff also found that the cells of Spirogyra 

 underwent amitotic division on loss of tone due to numbers of associated 

 bacteria and other organisms. The published accounts of the mitosis in 

 Spirogyra are not in agreement, but it is very probable that such discrepancies 

 as occur are due to differences of interpretation of the same phenomena and 

 perhaps also to defective technique. McAllister (13) has shown that in the 

 mitosis of Tetraspora lubrica ' the conduct of the chromatin in spireme forma- 

 tion, the origin and development of the spindle, and the mode of formation of 

 the cell-plate are processes the same as in Angiosperms. 1 



In the multicellular forms division may occur in any, or all, the cells 

 of the thallus, so that growth is to a great extent intercalary; or cell-division 

 may be restricted to the apical cell of each branch. In the Zygnemacese and 

 in the Siphonocladiales the transverse walls arise as a ring-shaped septum 

 which gradually extends inwards. On the other hand, the formation of the 

 cell-plate in Tetraspora and in (Edogonium begins between the daughter- 

 nuclei, and the wall extends outwards as in higher plants. 



In the Volvocinese the vegetative cells are provided with cilia, and the 

 zoogonidia and gametes of other groups are also ciliated. In the living 

 cell the cilia can but rarely be observed, and only when their movements 

 have become feeble or sluggish. A 2 per cent, solution of cocaine is often 

 useful in causing the cilia to come to rest. They can generally be well 

 observed by rapidly killing the cells by 

 means of 1 per cent, osmic acid or by 

 iodine solution. They can also be stained 

 by methods essentially similar to those em- 

 ployed in staining the cilia of Bacteria, 

 especially the tannin and carbol-fuchsin 

 method, which gives good permanent pre- 

 parations in which the cilia are stained bright 

 red. In the small sub-family of the Tetra- 

 sporeae the cells are peculiar in the possession 

 of motionless ' pseudocilia/ which in Apiocystis 

 Brauniana are sometimes very distinct and 

 can be plainly observed without staining. 



In the large group of the Conjugatse cilia 

 do not occur. 



The CHROMATOPHORES (which in all the 

 Green AlgaB are CHLOROPLASTS) are bright 

 green or sometimes yellow-green in colour. 

 The pigments are chlorophyll and xantho- 

 phyll, the former being as a rule greatly 

 in excess of the latter. With the exception 



Fig. 89. Escape of the zoogonidium 

 in (Edogonium; A, (E. Boscii 

 (Le. Cl.) Wittr. ; B, (E. Hirnii 

 Gutw. x 460. Each zoogonidium 

 possesses an anterior circlet of 

 cilia. 



w. A. 



