MORE ABOUT POLLINATION 



303 



pollinated plants the pollen 

 simply falls on the stigma ; grav- 

 ity is the agent of transfer. In 

 others, as in the fireweed {Epilo- 

 bimn), the style turns as it grows 

 so that it rubs against the an- 

 thers. There are some plants 

 whose cross-polHnation is accom- 

 phshed by means of water. 

 (Study Figure 126.) Snails, 

 where they are very abundant, 

 have been observed to act as 

 poUinators. 



h. As to the Stigma Pollinated. 

 — For some reasons it is more 

 important to note what stigmas 

 are pollinated than it is to note 

 what it may be that carries the 



pollen. 



Fig. 124. — Heads of dandelion. 

 At the left is an open head as 

 seen in the sunlight. At the 

 right is the same head as it is 

 at night. The bracts of the in- 

 volucre are of two kinds, short 

 outer ones (&) and long' inner 

 ones (6'). The opening and 

 closing is due chiefly to the 

 movements of the inner bracts. 



Fig. 125. — Cyme of syringa, or 

 mock orange. The terminal 

 flower blossoms first. Note that 

 the calyx is composed of sepals 

 which, for about half their 

 length, are united. 



If .it is the stigma of 

 another flower that the pollen 

 reaches, that is cross-pollination ; 

 if it is the stigma of its own 

 flower, that is close-polhnation. 

 Evidently these are two quite 

 distinct things. Close-polHna- 

 tion is also called autogamy. Of 

 cross-pollination there are two 

 kinds ; three if the polHnation of 

 one kind of plant by the pollen 

 of another kind be included. 



(i) The pollen may cross to the 

 stigmas of flowers of the same 



