ENGELMANN THE FLOWERING OF AGAVE SHAWII. 579 



The Flowering of Agave Shawii. 



By Dr. George Engelmann. 



In May, 1S76, Mr. Shaw received from San Diego, Cal., 

 through the kind offices of Messrs. Hitchcock and Parker, a full- 

 grown specimen of the fine species named for him. In June the new, 

 innermost, leaves became more slender and their marginal teeth 

 smaller. Early in July the flowering stalk began to rise. Regu- 

 lar measurements of its growth were made by Mr. Gurney, the 

 superintending gardener, at 7 o'clock a.m. and at 7 p.m., from 

 July Sth to September 5th. I have divided this period of 60 days 

 into 6 decades, and have added the mean temperature and the fall 

 of rain (at my station, 3 miles northeast of the garden) of each 

 decade. The oliowing table exhibits these data : 



AMOUNT OF GROWTH IN TEN DAYS. 

 1S76. 7 P.M. -7 A. 



July 8-17 2! i 



" 18-37 3 ' 



" 28-Aug. 6 4! ' 



Aug. 7-16 7 ' 



" 17-26 5 ' 



" 27-Sept. 5 4I ' 



July 8-Sept. 5 275 in. 19^ in. 46I in. 



The table shows that the night-growth (including the morning 

 hours) was in every decade larger than the day-growth, and in 

 the whole period surpassed it by 16 p. ct., the former amounting 

 to 5S, the latter to 42 p. ct. 



It is further seen that the largest advance was made about the 

 middle period, or from the 3rd o the 5th, and mostly in the 4th 

 decade. After Sept. 5th the growth diminished rapidly, about 

 the end of the month the head began to swell, and 3 months later 

 the first blossoms opened. 



The table also proves that the temperature of each decade did 

 not have any material effect on the growth of the stalk ; in the 

 warm weather of the first two decades it grew much less than in 

 the cooler 3rd period. 



