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) 
Fic. a ee eee wind, (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 
