34 FORMALDEHYDE. [CH. II 



alcohol as a decoloriser is avoided. The flowers must, 

 however, be boiled before being placed in the iodine fluid. 



(39) Formaldehyde. 



Loew^ and Bokorny^ have shown that although formal- 

 dehyde is poisonous even in very dilute solutions yet that 

 oxymethyl sodium sulfonate (which is easily decomposed 

 into formaldehyde and NaHSO^ can be used in culture 

 fluids, in the proportion of O'l per cent., without injury to 

 Spirogyra. Bokorny {loc. cit.) has shown that if Spirogyra 

 is cultivated, in the light, in a nutrient solution containing 

 0"1 per cent, oxymethyl sodium sulfonate, the starch in 

 the plant increases considerably, a result which we have 

 confirmed. The access of COo must of course be pre- 

 vented : for this reason the cultures must be examined for 

 moulds, or bacteria which might serve as a source of CO2 

 to the algae. The nutrient solution must contain OT 

 per cent, disodic phosphate to counteract the evil effects 

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

 plants must be compared with the control specimens 

 which have been grown under identical conditions but 

 without oxymethyl sodium sulfonate. 



(40) Starch-formers (leucoplasts). 



These may be examined in the tubers of Phajus 

 grandifolius, according to the method given by Stras- 

 burgerl The sections are to be placed in alcoholic 

 tincture of iodine diluted with half its volume of distilled 



1 Botan. Cejitralblatt, xliv. p. 315. 



2 Berichte d. D. Bot. Ges. ix. p. 103. 



3 Praktikum, pp. 67, 68. 



