72 Plant Tissue Culture 



stand for a few minutes (Step 2). For ordinary 

 routine washing of flasks used only for liquid 

 nutrients, the time required to transfer 50 flasks 

 from the draining table to the rinsing container 

 (Step 4 in the washing routine) is usually long 

 enough for flasks to stand in the acid. Flasks 

 which have contained solid residues likely to stick 

 to the walls should be left in acid over night. 

 After standing the requisite time, the flasks are 

 removed from the acid, using linemen's rubber 

 gloves, are drained thoroughly into the crock, and 

 are then placed on 18" X 24" enamel trays for 

 further draining (Step 3). While they are drain- 

 ing, a second batch of flasks can be immersed in 

 the crock of acid. After thorough draining on 

 the trays, the flasks are placed under running 

 warm water for a few minutes (Step 4). It is 

 important that all traces of bichromate be re- 

 moved (Richards, 1936, 452). They are then 

 rinsed thoroughly at least five times in running 

 tap water, twice in single-distilled water, and 

 finally once in double-distilled water, after which 

 they are inverted in paper-lined metal trays and 

 set aside to dry. Excess cleaning solution from 

 the draining trays can be poured back into the 

 crock at intervals. The acid should be replaced 

 by fresh whenever it turns green and ceases to 

 remove pencil markings on flasks without rub- 



