FORM-ALTERATIONS AND GROWTH OF CACTI. 35 



time one plant growing in the ground was marked and records kept for 

 comparison with those that had been taken up. The numbers used in 

 referring to these plants are the same as those used on pages 54, 58, and 

 61, and indicate the same individuals. 



Bisnaga No. 3 (see page 54). — On February 2 each rib was measured at 

 its base in approximately the same plane. In two cases the ribs were so 

 shrunken together that one measurement had to include two ribs. At 

 first the circumference continued to shrink slightly, losing 7 mm. by Feb- 

 ruary 12; after that it gained about 3 mm., and then remained practically 

 stationary until May 21, when measurements were discontinued. On 

 October 11 it was again measured and found to have gained 21.2 cm. in 

 circumference. On account of the plant being in the earth it was not 

 practicable to ascertain its weight at this time, but this increment in cir- 

 cumference represents an increase of 6 cm. in diameter, and since the 

 bisnagas shrink in all directions there was probably a similar gain in 

 height. 



Bisnaga No. 6. — On December 12, 1908, the whole circumference of about 

 132 cm. was marked off into intervals of two furrows each, measured from 

 the edges of the ridges, and measurements of these were taken at intervals 

 until May 21. During that time the circumference had lost 2 cm. Judg- 

 ing from the measurements, the circumference at times seemed to increase 

 slightly. This could hardly have been the case, for the plant was at this 

 time under the same conditions as the others which showed a constant loss 

 of weight. It might possibly be explained as due to a shifting of the in- 

 ternal pressure, so that the part of the circumference measured was actually 

 increased at the expense of some other part. When the plant was measured 

 again, October 28, 1909, the circumference had farther shrunk 2.3 cm., 

 making a total loss since December 12 of 4.3 cm.; and besides this it had 

 lost 4.1 cm. in height. This is offset by a loss in weight of 2,235 grams. 



The irregular outline of this plant makes any computation as to the 

 comparison of loss by weight and measure impracticable, but comparative 

 measurements and weights of Nos. 6 and 9 show that the loss in circum- 

 ference does bear a fairly direct proportion to loss in weight. From Janu- 

 ary 25 to May 21 No. 6 lost 2 cm. in circumference, while No. 9 lost 13 

 cm., or 6.5 times as much. During the same period No. 9 lost 6.33 times 

 as much weight as No. 6. On the other hand, an effort was made with 

 two plants to estimate loss in circumference by the measurement of a 

 small portion of the same. This method was found to be totally unre- 

 liable, as the proportions of loss in weight and circumference, during the 

 time of measurement, were completely reversed (p. 58). 



Bisnaga No. 9, which served in the experiment for effect of insolation, 

 was placed in the ground after losing 4.840 kg. Up to May 21 it had lost 

 approximately 5.238 kg. in weight and 13 cm. in circumference. On 



