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CHEMICAL AGENTS AND GROWTH 



day, 10 similar cuttings will be taken from all the lots and rooted under 

 identical conditions. Figure 7 gives the root counts obtained 3 weeks 

 after the cuttings were made. It shows that, although the cuttings were 

 all rooted under the same conditions, the number of roots produced 

 varied according to the treatments which had been given to the stock 

 plants. In other words, the cuttings "remembered" under which photo- 

 periodic regime they had been before being cut away from the plant. 

 This "after effect" had already been clearly shown by Waxman 

 (1957). One of his data was used in Fig. 8A, which gives the average 

 number of roots produced on cuttings of Cornus florida rubra taken 

 from plants which had been subjected previously to the indicated 



LEAF NUMBER 



IN 1956 



HOURS 



9 



OF 



12 15 18 

 LIGHT GIVEN 



9 12 IS le 

 IN 1955 



Fig. 8. Cornus florida rubra. A: average number of roots produced 

 after 80 days by cuttings rooted under the same 18-hr photoperiod but 

 taken from comparable side shoots of plants maintained previously for 

 125 days under 9-, 15-, and 18-hr days. Averages of 10 replicates per 

 treatment. B and C, average shoot length (B) and leaf number of (C) 

 produced under a uniform photoperiod in 1956 by large dogwood plants 

 having received the indicated treatments in 1955. Averages of 10 

 measurements (from Waxman's data, 1957). 



