ALG^E 61 



ing out from them, which unite to form a tube con- 

 necting the cells (Fig. 13, A, B, C). Sometimes the 

 protoplasm of one of the cells passes over into the other 

 one and fuses with its protoplasm ; or the protoplasm 

 may leave both cells and unite in the middle of the 

 connecting tube. In either case the result of the fusion 

 is the formation of a thick- walled resting-spore (zygo- 

 spore). This process of conjugation is characteristic of 

 the whole order, and, except in the very lowest forms, 

 consists in a fusion of the cell-contents only, the wall of 

 the resting-spore being an entirely new one. 



THE CHAKACE^ 



Probably no group of green plants is more puzzling to 

 the systematist than the Characese, or stone-worts, as 

 they are sometimes called, on account of the heavy coat- 

 ing of calcium carbonate frequently deposited in their 

 outer cell-walls, which renders the plant rigid and 

 brittle. These curious aquatics are all closely related 

 among themselves, but show no very obvious affinity 

 with any other group of algse, and at present all 

 attempts to connect them with the other algse are little 

 better than mere conjecture. 



All the Characese are characterized by the regular 

 division of the axis into nodes and internodes which 

 bear a definite relation to the first divisions in the large 

 apical cell which terminates each growing shoot. The 

 plants are remarkable for the great size of the inter- 

 nodal cells, which often reach a length of several centi- 

 metres with a diameter of a millimetre. The protoplasm 

 of these long cells shows a very active rotation within 



