1893 EXPERIMENTS OX HELIOTEOPISM 325 



The results clearly showed that the germmating 

 power of the seeds was hardl3% if at all, affected either 

 by being exposed to the Yacutim or to the atmo- 

 spheres of the various gases and vapours. Further, in 

 no single case, in the hundi-eds of seeds so treated, 

 did the plants produced from them differ from the 

 standard types grown from the control seeds even in 

 the smallest degree. 



The second paper described experiments in heho- 

 tropism, which had been undertaken by Mr. Eomanes 

 with the object of ascertaining whether plants would 

 bend towards a hght that is not continuous, but 

 intermittent. 



Mustard seedhngs, grown in the dark until they 

 were about one or two inches high, were used in all 

 the experiments ; they were either placed in a dark 

 room and exposed to flashes of hght in the fonn of 

 electric sparks passed at regular intervals, or thej" 

 were put in a camera obscura, before which was 

 placed a Swan bimier or arc lamp, the hght from 

 which was rendered intermittent by the regular 

 opening and shutting of the photographic shutter. 

 The hehotropic effect on the seedhngs was found in 

 all cases to be very marked, the most vigorous ones 

 beginning to bend towards the Hght ten minutes after 

 the flashing began, bending through 45^ in as manj- 

 minutes, and often through another 45" in as many 

 minutes more. By protecting half of the seedlings 

 from the interrupted hght, by means of a cardboard 

 cap, then after the experiment uncovering them and 

 exposing that half for the same dm-ation of time to 

 constant sunhght, Mr. Eomanes found that the bend- 

 ing was less in this latter case, that is, when the hght 

 was continuous. This result was confirmed by 

 placing two sets of plants under exactly similar con- 

 ditions before a Swan burner, the hght from which 

 was constant for one set of seedlings, and rendered 



