THE COLOURS OF ANIMALS AND PLANTS 147 



effects cross-fertilisation regularly, and humble bees 

 were actually watched in the act of fertilising by 

 Hermann Miiller. He saw them insert their heads 

 into the flower and emerge with the pollinia attached, 

 visit other flowers on the same spike, where they 

 tried, more or less ineffectually, to rub off the pollinia, 

 and finally fly off to other plants. Out of 97 

 humble bees which he caught, 32 bore the pollen 

 masses of orchids. He proved that the bees visit 

 the flower to obtain the fluid in the nectary, the 

 walls of which they pierce with their maxillae. 

 Moreover, he timed the bees and found that they 

 spent three or four seconds at each flower ; two or 

 three seconds being sufficient to fix the pollinia. The 

 average time spent at a given spike of flowers was 

 twenty to twenty-two seconds, the bees then flying 

 to another spike. In twenty-five to thirty seconds 

 the pollinia were depressed and cross-fertilisation 

 ensured. 



The beauty and odour of flowers and the storage 

 of honey are thus due to the existence of insects, and 

 in a large number of cases the actual insects are 

 known which effect cross fertilisation. Such is the 

 case with regard to all conspicuous flowers : honey is 

 secreted in order to attract insects, and the flowers are 

 large and conspicuously coloured, so as to be readily 

 seen by them. A striking illustration of this is seen 

 in the common Clover. Darwin showed that by 

 protecting 100 flowers with a net, not a single seed 

 was produced from them ; whereas the 100 flowers 

 which were outside the net were visited by bees and 

 produced 2720 seeds. Hence, but for humble bees, 



