THE ALGH 221 
plasmolysis. It is an excellent illustration of osmosis and is easily 
demonstrated in many eells with thin walls and rather watery 
protoplasts. 
281. Sexual Reproduction of Spirogyra. — Cut off with the dissect- 
ing scissors very small portions of material from the yellowish uneven 
filaments of Spirogyra which are often found clinging together. 
Fig. 155. Conjugating Filaments of Spirogyra. 
(Considerably magnified.) 
A, beginning of the process; B, the same filaments in a more advanced 
stage of spore-formation. The cells at a@ in each portion of the 
figure are at an earlier stage of conjugation than those at b. 
n, nucleus; c, chloroplast. 
Mount in a little water, without disturbing the relative position of 
the filaments, and examine first with m.p., then with h.p. Note: 
(a) Filaments lying paired, as in Fig. 155, B, connected by con- 
jugating tubes. 
(b) Filaments in which the tubes have not been fully formed but 
appear only as projections (Fig. 155, A, a). 
(c) The formation of ellipsoidal bodies, zygospores, by the union 
of the protoplasts of two conjugating cells. 
(d) Intermediate stages between cells in their ordinary condition 
and cells containing a single zygospore or entirely emptied of their 
contents. 
