624 The Outline of Science 



Plant is the goat, which is not a native of the plant's original 

 home in South America. We know, too, that repeated move- 

 ment is actually harmful. A plant which had been stimulated 

 twelve times daily for three weeks attained to only one-third of 

 the height of another left undisturbed. It was handicapped in 

 assimilating power, but probably, in addition, the constant irrita- 

 tion upset its constitution in some profound way. Is it better 

 to take the chance of being eaten or the certainty of being 

 stunted? 



The reaction to shock brings with it clear advantages in 

 other cases. The leaf of the Venus fly-trap folds quickly together 

 on the slightest touch of one of its sensitive hairs. In nature the 

 touch is that of an injudicious insect which is subsequently 

 crushed, drowned, and digested. The little filaments or stalks 

 of the stamens of the cornflowers contract instantly by 30 per 

 cent, when touched. The result is that the anthers, from which 

 the pollen has been shed, are pulled down over the brush of the 

 stigma, and the pollen is swept out and exposed to visiting insects 

 which carry it to other flowers. The bilobed stigma of the musk 

 closes on the pollen. In this case, and in others like it, the move- 

 ment has an obvious biological advantage. 



Do Plants Sleep? 



As night falls, the trefoil leaves of the clover fold their 

 leaflets up, the daisy flower closes, the tulip becomes once more 

 a bud, the leaflets of the wood-sorrel droop and close: the plants 

 sleep. The term sleep, consecrated by long usage, is not a happy 

 one, for with the sleep of animals this movement has nothing to 

 do. It brings no recovery from a non-existent fatigue. It is in 

 reality an active movement, not a collapse. Only in the seeming 

 relaxation recurring as darkness comes on is there a superficial 

 resemblance to the real relaxation of the animal and to the droop- 

 ing of its drowsy lids. 



The tulip flower, like that of the crocus, closes as the air 



