276 



BOTANY. 



Fig. 163.— Magnified fragment 

 of a leaf of a Dicotyledon, show- 

 ing reticulated venation. 



studied by macerating them so as to remove the soft tissue, 



leaving onyl the fibro-vascular 

 bundles. While there is, as a 

 rule, a general likeness between 

 them, there is yet an almost 

 infinite diversity in the details 

 of structure. The general dis- 

 position of the smaller veins is 

 well illustrated by Fig. 163. 



524. A great many Dicotyle- 

 dons show adaptations for pol- 

 lination by insect agency, and it 

 is safe to say that more than 

 half the species are more or 

 less dependent upon the visits 

 of insects in order that their ovules may be fertilized. 

 In a general way it may be said that the showy flowers 

 with a bright calyx or corolla, or both, are pollinated by 

 insects, while those without showiness are wind-pollinated, 

 or close-fertilized. The plants of the apetalous species are 

 for the most part not visited by insects; few of them have 

 bright colors, and few produce nectar. 



525. The simpler Choripetalse, as the Crowfoots (Fig. 

 164) and their near allies, attract insects by their showy 

 perianth, and the nectar they secrete. Cross-fertilization 

 is generally secured by a difference in the time of maturity 

 of stamens and pistils (i.e., by dichogamy), apparently, 

 however, often permitting close fertilization. The same 

 is true in general of most of the regular flowered Chori- 

 petalse. Thus in the Eoseworts (Fig. 165), while nectar 

 is usually abundant and the flowers are generally sweet- 

 scented as well as showy, their regularity of form prevents 



