THE ALG.E 



221 



plasmolysis. It is an excellent illustration of osmosis and is easily- 

 demonstrated in many cells with thin walls and rather watery 

 protoplasts. 



281. Sexual Eeproduction 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 o£ the process ; B, the same filaments in a more advanced 

 stage of spore-formation. Tlie cells at a in each portion of the 

 figure are at an earlier stage of conjugation than those at 6. 

 n, nucleus ; c, chloroplast. 



Mount in a little water, without distui"bing the relative iiosition of 

 the filaments, and examine first with m.p., then with h.p. Xote : 



(n) Filaments lying paired, as in Fig. 1.55, B, connected by con- 

 j'ugatinff tubes. 



(J) Filaments in which the tubes have not been fully formed but 

 appear only as projections (Fig. 155, A, a). 



((•) The formation of ellipsoidal bodies, zygospores, by the union 

 of the protoplasts of two conjugating cells. 



(rf) Intermediate stages between cells in their ordinary condition 

 and cells containing a single zygospore or entirely emptied of theii 

 contents. 



