Chapter VI 

 HOW CULTURES ARE STARTED 



As we have already seen, the two types of plant 

 material which have so far proved most useful in 

 plant tissue culture work have been, first, root 

 tips and, second, cambium or procambium. Most 

 of the following discussion will apply to these 

 types. 



Seedling roots. Root tips are perhaps sub- 

 jected in nature to more environmental vicissi- 

 tudes than are any other types of meristems. 

 They are, therefore, relatively resistant to injury. 

 Nevertheless, once a root is growing either in the 

 soil or in a culture medium, if it is not already 

 aseptic it cannot be rendered so by any but rather 

 drastic means which may well influence its subse- 

 quent behavior. It is, therefore, important that 

 roots for culture be obtained wherever possible 

 from sterile seedlings and, moreover, it is highly 

 desirable that the seeds themselves be rendered 

 aseptic with as little chemical interference as pos- 

 sible in order that consideration of potential after- 

 effects need not enter into the interpretation of 

 results. In many cases, aseptic seeds can be ob- 



