i8o 



Introduction to Botany. 



provide for the allurement of insects by offering them nectar 

 and pollen for food, and for attracting their attention by 

 means of odors and bright colors ; and at the same time they 



have had so to con- 

 struct and arrange 

 their parts that in- 

 sects in securing food 

 would necessarily 

 carry the pollen from 

 one flower to the 

 stigma of another. 



130. Allurement 

 by Pollen. Some 

 flowers secrete no 



FIG. 96. 



Pistillate and staminate flowers of Vallisneria spiralis. 



On the right a staminate flower has floated against nectar but offer an 

 the pistillate flower and an anther is touching one abundance of pollen, 

 of the stigmas. After KERNER. 



Roses, Anemones, 



and poppies are of this sort. Flowers of this kind are 

 more or less erect so that the pollen may not fall out, and 

 the stamens are usually numerous. Insects which feed on 

 the pollen of such flowers are certain to get their bodies 

 dusted over, and in this way they carry the pollen from 

 flower to flower. 



131. Allurement by Nectar. Nectar is the most com- 

 mon and most important allurement for insects. It is a 

 more or less watery solution of sugar, and of certain salts 

 and aromatic substances, secreted by a special tissue known 

 as the nectary, and expelled at the surface by transfusion 

 through the epidermis, by breaking down of the tissues, or 

 through a special opening of the nature of a stoma. The 

 nectar either remains clinging to the surface of the nectary 

 or it gathers in large drops and falls into a nectar recepta- 

 cle provided for it, as in the case of -violets, where horn- 



