FORM-ALTERATIONS AND GROWTH OF CACTI. 



33 



but two plants which had been uprooted and exposed to the sun at the 

 same time and were drying up did exhibit a very marked response to inso- 

 ation. These were Nos. 9 and 10, described on pages 61 and 63. 



Bisnaga No. 9. — On January 6 the plant was taken from the porch 

 where it had been standing- and placed on a stone wall near the south side 

 of the laboratory, in the full sun. Intervals were marked all the way 

 around. At first some of those on the north increased slightly, but after 

 January 19 every interval contracted. Fig. 14 shows two curves constructed 

 from the data furnished by this plant, N showing the contraction of an 

 interval on the north and ^ on the sotith side of the plant. The interval 

 most directly north contracted 20 and that most directly south 48 units, 

 while the sum of the contraction of the intervals on the north was 145 and 

 on the south 213 units. 



£60 



S — 



250 

 240 

 230 

 220 

 210 



N-- 



200 



190 

 180 



Fig. 14. — Two curves, N from measurements of a northern, and 5 from a 

 southern interval on bisnaga No. g. January 6 to May 21, igog. 



Bisnaga No. 10. — This plant stood within 6 inches of the south wall of the 

 laboratory. On November 17, 1908, three intervals were marked. No. I on 

 the side away from the wall, No. II on the side next the wall, and No. Ill 

 between them on the east. It was left in this position until January 2. 

 During this time No. I lost 22 units. No. II lost 10 units, and No. Ill lost 

 17 units. On January 2 the plant was turned around so that No. I faced 

 the wall, II away from the wall, and III the west. As would be expected, 

 II began to contract much more rapidly than before. The rate of con- 

 traction also increased in III, though to a lesser degree, but No. I actually 

 expanded until January 22, gaining 8 units, and at the end of the experi- 



