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 Stramoniwm) , 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 the 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 
