30 FORMALDEHYDE. [CH. II, 



posed into formaldehyde and NaHSOs) can be used in 

 culture fluids in the proportion of 01 per ceat. without 

 injury to Spirogyra. 



Bokorny {loc. cit.) has shown if Spirogyra is cultivated 

 in the light in a nutrient solution containing 0"1 per cent, 

 oxymethyl natrium sulfonate that the starch in the plant 

 increases considerably, — a result which we have confirmed. 

 The access of CO2 must of course be prevented : and for 

 this reason the culture fluids should be examined for 

 moulds, bacteria, &c., which might serve as a source of 

 CO2 to the algse. The nutrient solution must contain 

 O'l per cent, dinatrium phosphate to counteract the evil 

 effect of the NaHSOs set free. After four or five days the 

 plants must be compared with control specimens which 

 have not been supplied with oxymethyl natrium sulfonate, 

 but have been in otherwise identical conditions. 



(40) Starch-formers (leucoplasts). 



These may be examined in the tubers of Phajus 

 grandifolius, according to the method given by Stras- 

 burger^ The sections are to be placed in alcoholic 

 tincture of iodine diluted with half its volume of distilled 

 water. The relative positions of starch-former and starch- 

 grain and the elongated crystalloid are well shown in 

 Strasburger's figure 29. The leucoplasts in the rhizome 

 of Iris germanica are given in his fig. 30. 



Section B. The Evolution of Oxygen. 



(41) Bubbles of gas given off. 



Place a branch or two of a submerged water- 

 plant, such as Hottonia, Potamogeton crispus, or Elodea, 

 ' Praetieum, pp. 67, 68. 



