ri.AXTS AND INSECTS 



and the bright color of the corolla, are contrivances made 

 by the flower in its own interests; that is, to accomplish 

 the fertilization of the flower. Such flowers are, he 

 says, fertilized by some one species of insect or by sev- 

 eral species, and the insects in approaching the nectar 

 brush pollen from the anthers with various hairy parts 

 of their bodies and convey it to the stigma. Sprengel 

 did not, however, perceive the advantages the plant 

 gains, further than the mere formation of the seed. 

 Knight and Herbert, two later workers, perceived, in a 

 degree, the effects of this fertilization of plants by in- 

 sects upon subsequent plant generations. 



It remained for Darwin to place the almost forgotten 

 work of Sprengel upon a broad basis. " jSTo organic- 

 being fertilizes itself for a perpetuity of generations, 

 bnt that a cross with another individual is occasionally, 

 perhaps at long intervals, indispensable." Darwin fur- 

 ther showed that, in higher forms and the greater num- 

 ber of lower animals, the sexes are separate ; that those 

 forms having the function of the two sexes present 

 in the one animal, even these pair regularly. Breed- 

 ers of animals and cultivators of plants have found 

 that continued in-and-in breeding deteriorates the stock, 

 while crossing with another breed or another strain of 

 the same breed increases the strength and productiveness 

 of the offspring. 



Since continuous close-fertilization is detrimental to 

 the interests of the plants, Mature has brought about 

 contrivances to prevent such recurrence. She does this 

 in two ways: (1) by modifications in the structure of 

 the flower so that the pollen cannot possibly fall upon 

 the stigma of its own pistil; (2) in other plants, whose 



