ALGE 61 
ing out from them, which unite to form a tube con- 
necting the cells (Fig. 18, 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 CHARACEA 
Probably no group of green plants is more puzzling to 
the systematist than the Characee, 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 alge, and at present all 
attempts to connect them with the other alge are little 
better than mere conjecture. 
All the Characee 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 
