678 LIGHT AND LIFE 



after a single long night (cf. 7, section C) are more critical. One 

 such experiment will be described. 



The basic medium employed was 0.8 X Hutners with 1^ su- 

 crose; the temperature was 26 °C. Photoperiods of 10 hours were 

 given with 10 footcandles of cool white fluorescent light; for non- 

 inductive cycles, the 14-hour nights were interrupted in the middle 

 with 50 minutes of dim (1.5 kiloergs X cm~" X niin— i) red fluores- 

 cent light. At the start, series of 50-ml erlenmeyer flasks containing 

 20 ml of medium with 1/10, 1/3, 1, or 3 X the normal iron level 

 were inoculated with two 3-frond colonies from plants previously 

 grown for three days under long-day conditions on a mediuin with 

 no added iron. All cultures then received 2 non-inductive cycles 

 followed by one iniinterrupted (long) night. Within two hours of 

 the end of the long night, all were transferred to full-iron medium, 

 and then grown for four more non-inductive cycles, after ^vhich they 

 w^ere dissected. Fronds were counted on three occasions: before the 

 first non-inductive cycle; immediately after the long night; and at 

 dissection, when the number was 65 to 90 per flask. It w'as thus 

 possible to compute MR values for growth in each flask on the differ- 

 ing pretreatment media and growth on the full-iron medium after 

 the long night. Means of these values with their confidence limits, 

 and the means and ranges of the corresponding FL% values, are 

 shown in Table 1. They indicate clearly that growth in the media 

 with 1/10 and 1/3 the normal iron level before and during the long 

 night essentially eliminated flower induction, although growth after 

 the long night was in full iron medium. In addition, the 1/3 level 

 of iron had no significant effect on MR, and the 1/10 level affected it 

 only during the pretreatment. These results, and those of similar 



TABLE 1 



Effects of Various Iron Levels before and during a Single Long Night 



{LN) ON Flowering {FU}^) and Frond Multiplication Rate {MR) of 



L. perpiisilla 6746. See Experimental, A3. Exp. 1-14-60 



MR (3-7)'' at 

 Iron level (mg/L) M RiQ-'hY normal iron level: FL^^c day 7" 



day 0-day 3 to end of LN LN to dissection 



59.8 (3 X normal) 165.0 158.4 12.8(11-14) 



19.9 (1 X normal) 165.2 162.0 11.6(9-14) 

 6.6 (1/3 X normal) 163.8 161.8 0.8(0-3) 

 2.0 (1/10 X normal) 135.4 154.4 0.0 



» Means of 5 cultures. 95';; confidence limits calculated by analysis of variance on 

 all 20 values: ±10.1 



'' Means of corresponding 5 cultures. Confidence limits: ±8.8 

 ■= Means and ranges of 5 cultures. 



