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THE POPULAR SCIENCE MONTHLY 



value of the great water-balances described in the life of the plant, and 

 one naturally asks the question as to how long an individual might 

 survive at the expense of its great accumulated supply, and what activity 

 it may carry on while cut off from the customary supply of soil moisture. 

 The replies to these queries vary widely with the species considered. 

 The tree cactus may live a year or as long as two years in the open in 



Arizona upon its balance. Growth 

 and reproduction are in the main 

 inhibited, however, by any notable 

 depletion. Sometimes, however, the 

 death of the main trunk of a plant 

 leaves a living branch held high in 

 the air, and this may bloom, but 

 this action must be due to the 

 special stimulation of approaching 

 death. (Fig. 4.) The melon 

 cactus may survive one or two sea- 

 sons in the open, although when 

 given some shade individuals have 

 been seen to live three years, carry- 

 ing on some apical growth and 

 flower formation with the usual 

 rhythm. The prickly pears sur- 

 vive, grow and carry on reproduc- 

 tion for even longer periods. 



So far as physiological useful- 

 ness is concerned, stores of water 

 accumulated in tubers, bulbs or 

 thickened underground organs are 

 far more effective than thickened 

 aerial stems or leaves in holding a 

 water-balance available to the plant 

 for extended periods. Ibervillea, 

 the " guarequi " of Sonora, has a 

 thickened stem homologous with 

 the "Big Boot" of California, 

 which is a relative, and it has been cited many times to illustrate ob- 

 servations of an individual which is still alive although detached from 

 a supply since 1902, and has not received any notable addition since 

 1901. (Fig. 5.) The corms of Brodicea form new small corms during 

 desiccation, which are plump with the diminished supply on hand, and 

 this process continues until the balance reaches the vanishing point in 

 three or four years. The observations of Frofessor Campbell show that 

 plants with so little external appearance of water-storage as the liver- 



Fig. 5. An Individual of Ibervillea 

 sonora which has produced Vines and 

 Flowebs while isolated. This may be 

 repeated many seasons. 



