in.] THE FERTILISATION OF FLOWERS. 57 



the plant to be open during the day-time. For the 

 same reason plants which depend upon the bees and 

 butterflies close their petals as soon as the sun sinks 

 in the west. Then, too, observe the manner in which 

 various flowers are hung on the stalk in order to 

 protect their honey from deterioration by the access 

 of rain ; or those flowers in which the honey is not 

 thus protected such as the Daisy and Pimpernel 

 how they close their petals at the approach of rain. 

 Such researches have proved an intimate connection 

 between animals and, plants which previously seemed 

 to lack the most shadowy relation one to the other. 

 What, for instance, could seem more ridiculous than 

 the assertion that the clover-crop in any district 

 depends upon the number of old maids there? Yet 

 such is really the case, for the clover is dependent 

 chiefly upon the humble-bees for fertilisation in fact 

 one species, the red clover, is fertilised by humble- 

 bees alone. Now it is well known that the nests and 

 combs of humble-bees are pillaged and destroyed 

 by field-mice, which in turn are destroyed by cats. 

 The number of cats in a district is largely determined 

 by the number of old maids there resident, so that 

 if in a given district there are a large number of old 

 maids, there will also be a good supply of cats. If 

 a good supply of cats the field-mice will be held in 

 check and their numbers reduced. If field-mice are 

 not abundant the humble-bees will thrive, and ferti- 

 lise more clover. There seems at first sight some- 

 thing humorous about this connection, yet there are 

 many similar instances which Mr. Darwin has brought 

 to light. 



