Electrical Control of Polarity in an Egg 113 



54 (2014) 



Electrical control of polarity in an egg. 

 By E. J. LUND. 



[From the Puget Sound Marine Biological Laboratory and the 

 Department of Animal Biology, University of Minnesota, 

 Minneapolis, Minnesota.] 



The egg of Fucus in flatus is normally shed into the water after 

 low tide. The previous period of exposure to drying during low 

 tide can be imitated by wrapping plants in paper and leaving for 

 about twelve hours, then removing the tips of the plants, which 

 bear the reproductive organs, and floating them in dishes of sea 

 water 1 . 



The shedding of the eggs ican then be allowed to take place upon 

 thin cover glasses to which the eggs adhere securely in about six 

 'hours. One of the two cells of the first cleavage gives rise to the 

 frond while the other gives rise to the holdfast. Therefore such 

 a preparation fulfills ideally the necessary conditions for deter- 

 mining the orienting effect of a direct electric current of proper 

 density, upon the longitudinal axis of symmetry in the future 

 plant body. 



The cover glasses holding the eggs were placed in the bottom 

 of a special glass trough, through which flowed fresh sea water 

 and an electric current of appropriate density. The threshold 

 value of the fall of electrical potential through an egg, necessary 

 for orientation of the first cleavage is definite and amounts to 

 about .035 volt. Perfect orientation and normal growth only 

 occurs within a relatively narrow range of electrical potential 

 which lies around .025 volts. Higher potentials inhibit cleavage, 

 stop growth or kill the egg. It seems permissible to conclude 

 that the establishment of an electrochemical polarity in the egg 

 is probably an associated condition for the development of mor- 

 phological polarity, because the physiological mechanism which 

 determines morphological polarity can be controlled and directed 

 by an electric current of external origin. Direct evidence of the 

 existence of such inherent potential differences along the axis 

 in certain eggs 2 and tissues 3 already exists. 



1 Hurd, A. M., Bot. Gaz., 1920, lxx, 25. 



2 Hyde, I. H., Am. Jour. Phys., 1904, xii, 241. 



3 Lund, E. J., Jour. Exp. ZooL, 1921, xxxiv, 471. 



