SPIROGYRA. 265 



and ditches and consisting of unbranched filaments which 

 are slippery to the touch and are often frothy owing to 

 entangled gas-bubbles. The filaments vary greatly in thick- 

 ness (from about O'Ol mm. to 0*15 mm. in the British 

 species), but in the larger species it is easy to see with a 

 pocket lens the characteristic spiral chromatophores in the 

 cylindrical cells of the filament. 



379. Culture Methods. Some trouble is necessary 

 in order to keep Spirogyra in healthy growth indoors 

 the smaller kinds keep better than the larger ones, as 

 a rule. Metals are very injurious to Spirogyra, and it 

 is better to use rain-water instead of either tap-water or 

 distilled water in making up the culture solution. Knop 

 solution ( 184) of 0*1 or 0'2 strength may be used, 

 but the following formula gives better results with Spiro- 

 gyra : ammonium nitrate, 0*5 gr. ; potassium dihydrogen 

 phosphate, 0'2 gr. ; magnesium sulphate, 0'2 gr. ; calcium 

 chloride, O'l gr. ; ferric chloride, a trace ; water, 1 litre. 

 If it is necessary to use tap-water, let the tap run for 

 several minutes before taking what is required for the 

 culture. 



Use a small quantity of material a mass of Spirogyra 

 the size of one's finger is enough to place in 5 litres (about 

 a gallon) of the culture solution. Either keep the culture 

 in a large glass jar or aquarium, or place the material in a 

 number of large beakers set each beaker in a flower-pot 

 containing moist sand, so that the sand reaches nearly to 

 the rim of the beaker, cover with a glass sheet, and keep in 

 a cool room out of direct sunlight but in good diffuse light. 

 To obtain filaments free from starch (in order better to see 

 the pyrenoids), place a culture in a shaded place for a day 

 or two. 



In the culture solution the filaments will usually show 

 vigorous growth and cell-division. If after a week the 

 filaments are transferred to pure water and kept in bright 

 sunlight, conjugation will probably begin in about three 

 days. Material which has been kept in ordinary water or 

 culture solution may also be induced to conjugate by 

 transference to 2 per cent, cane sugar solution. 



