118 Plant Tissue Culture 



tained without any chemical treatment whatever. 

 This is true of all seeds which, when ripe, are en- 

 closed in fleshy, woody, or membranaceous fruits 

 (tomato, apple, squash, bean, tobacco, etc.). 

 Sound, clean fruits of these plants are opened by 

 breaking or tearing in such a way that no instru- 

 ment penetrates to the seed cavity. The seeds 

 themselves are then lifted out with sterile needles 

 or forceps, placed on slips of sterile paper in Petri 

 dishes, and allowed to dry under conditions which 

 will preclude the entry of contaminants from out- 

 side. These seeds can then be used for starting 

 cultures without further treatment (White, 1934, 

 65). 



Seeds contained in very small fruits, in drupes 

 or achenes, or the seeds of Gymnosperms cannot 

 be obtained in a uniformly aseptic condition by 

 mechanical manipulation alone. These must 

 therefore be surface-sterilized. Where ultra- 

 violet light is available, this may sometimes serve 

 as a sterilizing agent, but it is rather uncertain 

 since spores may easily become lodged in crevices 

 in the seed surface which are protected from illu- 

 mination even if the seeds are constantly shaken. 

 The most satisfactory result is to be obtained with 

 bromine gas (Klein u. Kisser, 1924, 299; Burlet, 

 1936, 207). Seeds are shaken for 5 to 10 minutes 

 in a bottle containing a few ml. of 1 per cent 



