EFFECTS OF EXPOSING SEEDS 



93 



on the bottom of the germinating dish. Over the center was placed 

 the radium-tube (lo mg., 1,500,000 x), with all the radium in the 

 lower end, and the tube in contact with the underljnng seeds. 



Control similarly arranged with empt}^ tube. 

 March i, 5 : 30 P. M. 



No seeds have germinated in either culture. 

 March 9, 9 A. M. 



The control seedlings are all of about the same height and color, 

 being normally green. Average height (estimated), 30 mm. 



The radiated plants are entirel}^ etiolated under the radium-tube, 

 and for a radius of 4 mm. on all sides. The height of the seedlings 



Fig. 6. Experiment 8. Retardation of Germination and Growth of Timothy Grass 

 by Radium Rays. Activity, 1,500,000. 



gradually increases from 3 mm. at the center to about 30 mm. at the 



circumference. 



March 10, 12 M. 



The exposed culture was photographed (figure 6). 

 March 11, 3 130 P. M. 



Microscopic examination of the control plants shows in the cells 

 of the leaves normal chloroplastids, with healthy, green color. 



In the non-green radiated seedlings, the plastids in man}' cells 

 were apparently of normal size and shape, but destitute of green, 

 while in other cells the plastids, although green, had largely lost their 

 shape and individuality, and were aggregated in a disorganized mass 

 against the vertical cell-walls, and often massed in one end of the cell. 



A similar result, though less marked, was obtained by exposure 

 made through eight layers of sheet tin, a total thickness of 9 mm. 



