ANIMALS AND PLANTS 245 



less. In such plants a large amount of pollen is neces- 

 sary in order that fertilization may be insured, as a very 

 large part of it fails to reach the carpels. An extreme 

 case of this is seen in the pines and firs, where the 

 amount of pollen is enormously in excess of what is 

 actually needed for fertilization. 



The development of contrivances by which the trans- 

 fer of pollen to the pistil is facilitated, results in an 

 obvious saving of pollen, and is in itself an advantage ; 

 but experiment has demonstrated that cross-fertilization, 

 i.e. pollination of one flower by pollen from ' another 

 one, is generally of advantage to the plant, as seed so 

 produced is usually more vigorous than when the 

 ovule is fertilized by pollen developed in the same 

 flower. 



The simpler flowers have no enveloping leaves, and 

 the first step toward the development of a floral en- 

 velope or perianth was probably the production of 

 small scale-like leaves, either green or membranaceous 

 in texture. The change from these inconspicuous, 

 purely protective floral leaves, to those which are more 

 or less conspicuously colored, marks the next advance 

 in the evolution of the flower. This bright-colored 

 corolla would no doubt make the flower more conspic- 

 uous, and attract insects in search of pollen. Such an 

 insect visiting the flower would be pretty sure to carry 

 some of the pollen to other flowers of the same kind, 

 insuring cross-fertilization. As a result of natural se- 

 lection, it is easy to conceive how flowers having the 

 showiest corollas would stand a better chance of at- 

 tracting insects and thus being cross-fertilized. These 

 plants would produce a greater amount of seed, and in 



