1 88 THE BEGINNINGS OF LIFE. 



should understand that the branches of this plant are 

 made up of elongated, cylindrical, and transparent 

 cells, or internodes, of a greenish colour. On micro- 

 scopical examination it has been ascertained that the 

 colour is due to the presence, immediately beneath 

 the cell-wall, of a layer of green chlorophyll disks or 

 vesicles, each of which is about -r-^Vo" ^ n diameter. 

 These are uniformly distributed, except along a spirally 

 disposed line which is therefore colourless on each 

 side of the cell. In the situation of this line (along 

 which the green disks are absent), the c mucus ' or 

 protoplasmic layer has also less depth than it has over 

 other parts of the surface of the internode. The layer 

 of green disks lies., in fact, in the outermost or super- 

 ficial portion of the protoplasmic layer, whilst within 

 this is situated a colourless axial fluid. The inner 

 surface of the protoplasmic layer is irregular and under- 

 goes constant changes of form. It is these contrac- 

 tions of the mucus or protoplasmic layer, taking place 

 in a regular manner, which communicate their motion 

 to the contained fluid, and thus produce the so-called 

 c cyclosis 3 of the cell-contents. With these explana- 

 tions the reader will readily understand Mr. Carter's 

 description. He says: c All are aware that in the 

 fresh-water Algae commonly called Confervas, the for- 

 mation of the spore is preceded by a breaking up or 

 displacement of the cell contents, after which a con- 

 densation and rearrangement of them takes place, and 

 they are then invested with a capsule which remains 



