CHLOROPHYCEAE 



225 



The species found in running water will usually conjugate within 

 a week, when brought into the laboratory and placed in rain water or 

 tap water. Species belonging to quiet waters, when brought into the 



Fig. 49. — Spirogyra: A, vegetative cell of a large species, with four spiral chromatophores, con- 

 taining many large and small pyrenoids. B, a smaller species with only one spiral chromatophore. 

 C, union of gametes: these large, non-motile gametes, consisting of the entire contents of the cell, 

 are characteristic of the group. D, mature zygotes: the one on the right focused on the surface; the 

 one on the left focused for the center, showing the nuclei of the two gametes. All X300. From 

 Chamberlain's Elements of Plant Science (McGraw-Hill Book Co., New York). 



laboratory and placed in a 0.2 per cent Knop's solution, are likely to 

 undergo rapid cell division and growth. After the alga has remained in 

 such a culture for a few days or for a week, conjugation may be in- 

 duced by transferring to rain water or tap water, and keeping the cul- 

 ture in bright sunlight. Conjugation may begin within 3 or 4 days. 



