411] EH. 8. Johnston 218 
sidered, the values obtained being expressed as averages per 
plant, for each of the four-week periods. The temperature 
conditions, the evaporating power of the air and the intensi- 
ty of radiation were recorded for each of the two exposures, 
but these are left out of the present consideration. 
The results obtained from these three plant measurements 
are shown in the accompanying table, wherein all the values 
are expressed in terms of the corresponding value for the 
period ending May 22. In this table the dates of beginning 
and ending of the several culture periods are shown in the first 
two columns. Each value given in the table represents an 
average growth-rate representing a single plant, for a time 
period of 28 days. 
EXPERIMENTAL DATA 
Period Stem Total Total Av’ge of 
Beginning Ending Height. Dry Wt. Leaf Area Wt. & Area 
Feb. 14 Mar. 13 -73 -50 . 63 ST 
Feb. 28 Mar. 27 .83 .62 81 72 
Mar. 13 Apr. 10 85 72 77 75 
Mar. 27 Apr. 24 94: 80 -76 78 
Apr. 10 May 8 98 .89 .76 .83 
Apr. 24 May 22 1.00 1.00 1.00 1.00 
(67.5 em.) (1.338 g.). (213.5 sq. em.) 
May 8 June 5 93 sO 93 92 
May 22 June 19 83 93 98 96 
June 5 July 3 73 93 1.00 97 
(214.1 sq. em.) 
June 19 July 17 7 -88 .88 .88 
July 3 July 31 97 91 92 92 
July 17 Aug. 14 1.04 82 .83 .83 
July 31 Aug. 28 91 . 67 77 72 
Aug. 14 Sept. 11* — — — — 
Aug. 28 Sept. 25 1.07 76 70 73 
Sept. 11 Oct. 9 97 55 .58 57 
Sept. 25 Oct. 23 -78 34 43 39 
Oct. 9 Nov. 6 79 36 51 44 
The different kinds of growth-rates are seen to vary inde- 
pendently, from period to period, but two of the growth 
*Data not obtained because of insect injury to plants. 
