130 Elementary Botany 



the tube, which latter was given ofif from one of the cells (fig. 251), as we 

 have seen is the case with Gymnosperms. It is a question which requires 

 further investigation. 



As a general rule the pollen is not capable of fertilising the 

 ovules of the same flower, and hence has to be taken to another, 

 and the process known as cross-fertilisation is brought about. 

 The pollen is carried from flower to flower by various means. 

 The first agency we shall notice is the wind. In the Hazel, for 

 example, we have a monoecious plant with unisexual flowers. 

 It is evident that the pollen must be transferred from one flower 

 to another. The male and female catkins are on the same 

 plant (fig. 162), the former pendulous with numerous anthers 

 and a large quantity of pollen, the latter erect with the red 

 stigmas appearing through the enveloping bracts. When the 

 pollen is fully ripe it is shed from the anther cells and scattered 

 by the wind ; the greater portion is wasted, but some falls upon 

 the stigmas, fertilising them. Such a plant is said to be anemo- 

 philous, or wind-fertilised. Other examples of anemophilous 

 plants are to be found in the Oak, the Fir, the Yew, and various 

 Grasses and Cereals. In all these cases the flowers are small 

 and inconspicuous and destitute of odour, whilst the pollen is 

 produced in a far larger quantity than is actually needed for 

 fertilising purposes. Often in Fir forests the pollen is given off 

 into the air in such enormous quantities that it is washed down 

 by the rain as a yellow powder, and is popularly known as 

 sulphur rain. 



More important agents in the fertilisation of flowers are 

 insects. In all cases of insect-fertilised (entomophilous) plants 

 the flowers possess either rich and variegated colours, or sweet 

 odours, or have both qualities. These serve to attract the 

 insect, whilst in some part of the flower honey is stored up in 

 a nectary. Whilst endeavouring to obtain this the insect comes 

 into contact with the anther, and the pollen is scattered over 

 portions of its body, and, being carried away, adheres to the 

 glutinous stigma of the next flower visited. 



The mechanical contrivances and arrangements to ensure 

 this proper distribution of the pollen are very numerous. In 

 an elernentary book such as this it is only possible to notice a 

 few typical forms. 



