66 Elementary Work in Botany. 



seeds unless pollen from the same flower or another flower 

 of the same kind reaches the stigma. The flower is then 

 said to be fertilized* It has also been shown that usually 

 the best seeds are produced when the flower has been fertil- 

 ized by pollen of another flower. This is called cross- 

 fertilization. When stigmas receive the pollen of stamens 

 which are with them in the same flower we say the flower 

 is self -fertilized. Cross-fertilization is chiefly brought about 

 by insects; but grasses (wheat, corn, barley, etc., are in 

 the grass family), date-palms and most of our forest trees 

 are fertilized by pollen carried in the wind. The flowers of 

 such plants, having no use for signals, are without petals, 

 z. ., apetalous. Indeed, the flowers of oaks, poplars, and 

 pines are so inconspicuous that many people think these 

 trees are flowerless. A few inconspicuous flowers need the 

 help of insects. These bear nectar and attract insects by 

 their odor. Highly colored flowers and fragrant flowers 

 usually bear nectar, and are so constructed that their insect 

 visitors in getting the nectar must rub against anthers 

 when they are shedding pollen, and against stigmas when 

 they are ready to receive pollen. Thus, in the common 

 hollyhock, when the anthers are covered with pollen, the 

 stigmas are hidden in a tube formed by the filaments, and 

 after the pollen is shed the stigmas come out. Insects vis- 



* Pollen grains on the moist stigma send sprouts down through the style into 

 the ovary, where they come in contact with the ovules. Ovules not thus reached 

 do not grow. If the school is provided with Barnes' dissecting microscope the 

 shape and even the markings of pollen grains may be shown by combining 

 several lenses so as to reduce the focal distance to less than half an inch. 



