1913-14.] BOTANICAL SOCIETY OF EDINBURGH 291 



On the other hand, is the less growth of plants continu- 

 ally in the light due to a shorter growing region .' 



III. What is the comparative effect of these conditions 

 on the growing region of root and shoot i 



Methods. 



Beans were grown in tap-water cultures under four Beta 

 of external conditions of light and darkness : — 



I. Normal conditions, i.e. shoot in intermittent light 

 and darkness and root in the dark. 



II. Intermittent conditions, Le. shoot and root in inter- 

 mittent light and darkn— 



III. Darl;. — Both in the dark day and night. 



IV. Light. — Both in the light day and night. (Two 

 electric lights, one of fifty and another of twenty-five 

 candle power, were used at night, giving a diffuse light. > 



The temperature conditions were uniform for all the 

 experiments, with 19° and 24 : C. as limiting temperatures. 

 The humidity varied during the periods of experimentation 

 between -40 per cent, and 65 per cent. 



Experiments I. and II. were carried on during the 

 months of November and December, when the proportions 

 of light to darkness were 9-15 and 8-16 hours respectively : 

 numbers III. and IV. during February, when the pro- 

 portions were 10-14 hen 



The roots having an initial length of 20-30 mm. were 

 marked with Indian ink with a fine sable brush in 1 mm. 

 divisions, over a length of 15 mm. from the tip. then in 

 lengths of 5 mm. to the base. Daily measurement- : 

 growing regions and the total lengths of the roots were 

 recorded. 



The shoots were marked as soon as possible by hand in 

 5-mm. divisions from the growing point (as nearly as 

 possible) and in 1-mm. divisions towards the base of the 

 stem : afterwards a special marker was used, the familiar 

 rubber-wheel marker having proved unsuitable for the 

 particular purpose. I devised a flat rubber stamp gradu- 

 ated in 1 and 5 mm. — that is 15 mm. length over all. 



Care was taken to prevent desiccation or damage to the 

 organs while they were beino- marked or measured. 



