324 SOME SPECIAL ADAPTATIONS 



contact with the pollen-bearing portion of the insect's 

 body. It has been shown that even artificial pollination 

 of flowers of these species with pollen from the same type 

 of flower is unfavorable to seed production, this occurring 

 best when the pollen comes from the other type. 



590. A few plants (e.g. the common Dandelion, and 

 some of the Hawkweeds) whose structures would indi- 

 cate entomophily, and whose near relatives are so polli- 

 nated, seem to have dropped the habit of requiring polli- 

 nation, and the eggs develop without fertilization. Thus 

 we find a loss of sexuality in these plants (apogamy, 

 parthenogenesis) . 



591. In their methods of seed distribution also, the 

 Flowering Plants show great variation. Some seeds are 

 let fall directly from the parent plant, and are of such 

 structure that they are not suited to any special means of 

 distribution. The result is a crowding of the young seed- 

 lings, and competition between them and with the parent 

 plant. Such plants do not extend their range rapidly. 

 On the other hand a great proportion of the Flowering 

 Plants have structures, either of the parent plant or of 



the seed, that fit the seeds for special 

 modes of distribution. Depending 

 upon the habitat, and means of 

 seed distribution the spread of such 

 plants may be more or less rapid. 



592. The chief agents in seed 

 distribution are (1) water, (2) 



FlG ' 2 a 4 shr?o cUebur. thistle ' d ( 3 ) animals (including man), 

 and (4) mechanical expulsion. 

 Adapted to distribution by water are seeds (or fruits) 

 with an abundance of corky or woody tissue which 

 buoys up the seed, and, in the case of ocean-borne 

 forms (e.g. coconut), protects the seed from mechanical 



