Culture Techniques 



141 



tures is similar except that, for dividing the tissue 

 mass, a small, sharp scalpel gives better results 

 than do the scissors. 



Growth. Under ideal conditions, root cultures 

 set up as described above will begin to grow almost 

 immediately and will increase 3 to 4 mm. in length 

 in the first 24 hours. (For methods of measuring 

 growth, see later.) This increment rate acceler- 

 ates up to about the 5th day when average rates 

 of 10 to 15 mm. per day are common (occasional 

 roots may grow as much as 80 mm. per day for 

 single 24-hour periods), after which the growth 

 rate again decreases rapidly (Fig. 43). This re- 

 tardation indicates that the 5th or 6th day is the 



12 3 4 5 6 7 



Days 



Fig. 43. Typical increment rates of tomato roots (average of 



1000 cultures) on each day of a single one-week passage. The 



maximum increment rate is reached on the fifth day. 



