164 Plant Tissue Culture 



had much less experience with the method.) The 

 results were : 



Root Tru* A's B's A , B , 



length measure- measure- errQr errQr 



mm. ments ments 



Average 131 144 123 + 7.9 -13.3 



Error as per cent of true value = +6.0 - 10.2 



In this series the experienced observer tended 

 to overestimate the length of cultures by about 

 6 per cent, which is just about enough to compen- 

 sate for the systematic error of - 7.5 per cent due 

 to the presence of unmeasured branches (see 

 above), while the less experienced observer tended 

 to underestimate the lengths by a considerably 

 greater margin. In experienced hands, this 

 method will give results of an accuracy and relia- 



