EFFECTS OF EXPOSING SEEDS 



91 



Experiment 6 

 February 2, 6 P. M. 



Numerous seeds of timothy grass were scattered evenly over the 

 bottom of an earthenware germinator, and the glass tube of RaBrg 

 (10 mg., 1,500,000 x) was supported over the center of the dish with 

 the end containing the radium resting on the bottom among the seeds. 



A control was similarly arranged with an empty tube, and both 

 cultures were placed in the dark room. 



February 9, 10 A. M. 

 Radium 

 No seeds directly under the tube 

 have germinated. Germination has 

 begun about 2 mm. from the tube, 

 and plumules and radicles are short- 

 est near the tube, and increase in 

 length toward the edge of the dish. 

 There is a slight (in some cases, 

 marked) tendency for the plumules 

 to bend in toward the center. This 

 suggests a positive radiotropism^ but 

 is probably a hydrotropic response to 

 the more humid conditions at the 

 center of the germinator. 



February 11, 9 A. M. 

 Radiu7n 



The seeds at the center are be- 

 ginning to germinate, but slowly. 

 The following measurements of the 

 height of the shoots from the cir- 

 cumference to the center of the ger- 

 minating dish is typical : 10 mm., 9 

 mm., 6 mm., 2 mm., i mm. 



All the seedlings are decidedly 

 pale and those within a radius of 

 7.50 mm. are entirely etiolated. 



All the hypocotyls are excessively 

 elongated beyond the radius of ^ -$0 

 mm. from the center, making the 

 average height of the seedlings be-^ 

 yond this radius much taller than 

 those not radiated. 



Control 

 The seeds have germinated evenly 

 over the bottom of the dish, at the 

 center as well as elsewhere. No 

 tendency to bend toward the center 

 or in any other direction was ob- 

 served. 



Control 



All of the seedlings are of about 

 the same height and average much 

 taller than the radiated set. 



The seedliijgs are uniformly of a 

 dark green color, in striking contrast 

 to those of the radiated set. 



The heights of the shoots average 

 much less than those of the radiated 

 plants outside of the 7.50 mm. ra- 

 dius. 



