Volume 1 1 - Number 7 



The Plant World 



^ TOaiV'iiinr of Q^cucral ^ktanp 

 JULY 1908 



THE FLOWERING STALK OF THE 

 CENTURY PLANT. 



By Dr. W. B. MacCallum. 



During the past spring an unusually large number of 

 century plants, Agave Americaini, blossomed in the vicinity of 

 Tucson, and a record was obtained of the rate and amount 

 of growth of the remarkable flower shoot of two of these 

 plants. The individuals selected for observation grew in the 

 botanical garden of the University. One was measured daily 

 at the same hour as nearly as possible to obtain a record of 

 the daily increment, and the other was marked into zones 

 and measured occasionally, to determine the region of most 

 active elongation. The former plant was a rather large 

 specimen (Fig. i :) with a striking rosette of the character- 

 istic thick, succulent, erect leaves whose tips reached to a 

 height of 8 ft. <; in. above the ground. As the contents of 

 these leaves were gradually withdrawn to the stalk, there 

 was a marked decrease in volume, and also turgidity, accom- 

 panied by a loss of mechanical rigidity, until finally they were 

 quite flaccid and drooped,over to the ground. It would seem 

 that the great rigidity of these leaves lies in their high tur- 

 gidity rather than in any mechanical tissue they possess. 

 Ultimately there is a complete exhaustion of all contents 

 except the fibrous and woody parts, the leaves at last be- 

 coming quite dry and brittle. A leaf cut off before flower- 

 ing weighed 2910 grams. After flowering a similar leaf 



