1881 FLASHING LIGHT ON PLANTS 113 



such is the direction in which the explanation is to 

 be sought. I also think that the difficulty is mitigated 

 by the consideration that both the ganglion of the 

 spider and the sting of the wasp are organs situated 

 on the median Kne of their respective possessors, and 

 therefore that the origin of the instinct may have been 

 determined or assisted by the mere anatomical form 

 of the animals — the wasp not stinging till securely 

 mounted on the spider's back, and when so mounted 

 the sting might naturally strike the ganghon. But 

 I have not yet read Fabre's own account, so this 

 view may not hold. Anyhow, and whatever de- 

 termining conditions as to origin may have been, it 

 seems to me there can be little doubt that natural 

 selection would have developed it in the way you 

 suggest. 



I have now grown a number of seeds exposed to 

 the flashing light, but am not yet quite sure as to the 

 result. About one seedling out of ten bends towards 

 the flashing source very decidedly, while all the rest, 

 although exposed to just the same conditions, grow 

 perfectly straight. But I shall, no doubt, find out 

 the reason of this by further trials. It is strange 

 that the same thing happens when I expose other 

 seedhngs to constant light of exceedingly dim in- 

 tensity. It looks as if some individuals were more 

 sensitive to Hght than others. I do not know 

 whether you found any evidence of this. 



I have just found that this year again I have 

 been too late in asking them to send me cuttings of 

 the vine for grafting. I did not know that the sap 

 in vines began to run so early. 



I 



