636 proceedings: botanical society 



made to explain, besides the origin of the field, the secular variation 

 as it is actually observed. 



In conclusion it was pointed out that the solution of some of the 

 questions entering into the problem of the origin of the earth's magnetic 

 field must be deferred until the completion of the magnetic survey of 

 the earth now in progress under the auspices of the Carnegie Institu- 

 tion of Washington. 



Discussion. Mr. Burgess discussed the question of the effect of 

 pressure on magnetic properties of iron. Our knowledge of variations 

 in the magnetic conditions of ferrous materials is at present insufficient 

 to give much help. Mr. Swann referred to the difficulty associated 

 with the assumption of electric currents as the origin of the earth's 

 magnetic field primarily in the explanation of the e. m. f. to which 

 these currents owe their origin; this difficulty is not, however, as great 

 as may appear, for it is not improbable that the state of equilibrium 

 in the rotating earth might involve relative motion between the elec- 

 trons and the ordinary matter as a condition for the absence of degra- 

 dation into heat of such motion as exists. It is a known fact that the 

 intensity of magnetization produced in a sphere of infinite permeability 

 when placed in a magnetic field is only four times the intensity which 

 would be produced were the permeability only two; the reason for this 

 is to be found in the demagnetizing force which a magnetic sphere 

 produces in its own substance. It appears that the principle inherent 

 in the phenomenon is not limited to the case where the magnetizing 

 influence is an ordinary magnetic field but is of wide application, so that 

 we may say in general that it is impossible to produce, no matter what 

 the material of the sphere may be, an appreciable magnetization in a 

 sphere by feeble influence. J. A. Fleming, Secretary. 



BOTANICAL SOCIETY OF WASHINGTON 



The 112th regular meeting of the Botanical Society of Washington 

 was held in the Assembly Hall of the Cosmos Club, Tuesday, April 4, 

 1916. Fifty-two members and five guests were present. Harry R. 

 Fulton, George L. Keenan, Lester A. Round, J. F. Clevenger, 

 C E. Temple, A. E. Aldous, Victor Birckner, and Forrest S. 

 Holmes were elected to membership. The following papers were 

 presented. 



Botanical explorations in South America: J. N. Rose. 



Plants domesticated in Peru: 0. F. Cook. Mr. Cook gave a brief 

 account of the agriculture of the Incas, with their wonderful terraces 

 and system of irrigation. Among the plants domesticated by them 

 were maize, beans, lima beans, peanuts, quinoa (Chenopodium quinoa), 

 red peppers {Capsicum), mandioca, tomatoes, passion fruits, sweet 

 potatoes, tuberous Tropaeolum and Oxalis, arracacha (a celery-like 

 plant), squashes and pumpkins, gourds; and among the fruits were 

 chirimoyas, lucuinas, and pepinos. The narcotic coca, from which 

 cocaine is now prepared, was also grown. Mr. Cook's paper is embodied 

 in an article since published in the National Geographic Magazine, 

 29:474-534. June, 1916. 



W. E. Safford, Corresponding Secretary. 



