Nutrients 91 



1936, 235, 1939, 165), added, but in which these 

 synthetic adjuncts play only a secondary and ill- 

 defined role. Little is really known about the ex- 

 act constitution of such nutrients and, although 

 they are quite satisfactory for their primary pur- 

 pose of sustaining growth of isolated members, 

 their preparation is largely a matter of rule-of- 

 thumb. The successful use of such complexes by 

 the animal tissue culturists antedated by many 

 years the development of satisfactory plant tissue 

 culture media. Attempts were, of course, made to 

 utilize similar media for plant tissues but, as we 

 have already seen, these attempts all failed, with 

 the exception of the single unconfirmed piece of 

 work by Schmucker (1929, 110). This failure has 

 had as one consequence the forcing of investiga- 

 tion into a different channel and the slow, tedious 

 building up of a mass of information sufficient to 

 permit the designing of nutrients made up of well- 

 defined products of synthetic origin in place of the 

 ill-defined organic broths and juices. 



Plant tissue culture nutrients contain four cate- 

 gories of materials. These are, first, water ; sec- 

 ond, inorganic salts; third, organic constituents; 

 and sometimes, fourth, coagulating agents. 



Water. Since water makes up approximately 

 97 per cent of the mass of all nutrients, while some 

 other ingredients are required in amounts repre- 



