182 CHEMICAL AGENTS AND GROWTH 



MATERIALS AND METHODS 



Seeds of Pisum sativum, var. Alaska, were obtained from Asgrow, 

 Inc., of New Haven, Connecticut, sown in vermiculite (Mica-Gro 

 Type B, supplied by Piatt Seed Company, Branford, Connecticut, 

 thoroughly washed in running water) and allowed to develop for 7 

 days at 26 ± 1 °C. Experimental plants were either "dark-grown" or 

 "red-grown." The former were kept in darkness except for exposure to 

 dim green light at time of handling; these were selected for recurved 

 apical crooks. Red-grown plants were obtained by exposure to red 

 light (two 15-watt red fluorescent lamps at a distance of 30 cm, giving 

 approximately 19.5 kiloergs • cm - • min~^) for 20-min periods at 

 3-hr intervals during the 18 hr before harvest, and were selected for 

 approximately 90° apical crooks. 



All sections were taken from plants with third internodes 15-40 

 mm long. Most experiments were conducted with sections initially 8 

 mm long and cut 4 mm below the apex, but some were conducted 

 with 5 -mm sections cut either 1 or 6 mm from the apex in order to 

 obtain extremes of endogenous growth or of response to auxin or 

 gibberellic acid (see Purves and Hillman, 1958). Sections were 

 randomized in buffer after cutting, then distributed in lots of 10 on 

 circles of Whatman No. 1 filter paper in 10-cm petri dishes containing 

 8 ml of medium. The basal medium consisted of 0.02M KH2- 

 Na2HP04 buffer, pH 6.1, with 2% sucrose. Each dish was divided 

 into halves by a microscope slide under the filter paper; thus each 

 experimental treatment was given to two replicate lots of 10 sections 

 each. 



Measurements were made after a 20-hr growth period in darkness 

 (except for initial radiation treatments) at 26 °C. In certain experi- 

 ments, lots of sections were weighed before and after growth; most of 

 the data on fresh weight increase so obtained were similar to those 

 on elongation, with the exceptions to be noted. All radiation treat- 

 ments were given to the sections within the first 2 hr of the growth 

 period. Red-light treatment was for 100 min (approximately 1950 

 kiloeres/cm-); the effect so obtained was maximal, since even con- 



