PLANTS DEFEND THEMSELVES 41 



There are some plants which show their reason- 

 ing in a different method of defence against their 

 insect enemies. Knowing that at night they are 

 safe from the wingless pest, while the night moths 

 and their allied pollen-distributors will still be at 

 work, these plants open only during a few hours 

 of the night, and send forth into the darkness sweet 

 odours to call the flying messengers. These plants 

 usually develop no means of protection other than 

 the habit of night blooming: this provision is ade- 

 quate. An exception, however, is the Jimson-weed 

 (Datura Stramonium) , which not only emits a rank 

 odour to ward off unwelcome insects, but goes to 

 the further pains of covering its large fruit pods 

 with stout prickles. One of tKe most beautiful of 

 the night plants is the night-blooming cereus, which 

 has a perfume so strong and so sweet that it drowns 

 all other odours near it. 



A means of defence similar to that adopted by 

 the night-bloomers is shown by those plants which 

 bloom only in the early morning, when, because of 

 the dew-sprinkled ground, they know no insects 

 will be stirring. The rising sun warns them that 

 it is time to close, and, obedient to his warning, 

 they draw the shutters against the approach of the 

 gluttonous, crawling pests. 



The plants which avoid their insect enemies by 



