276 STRUCTURAL BOTANY 



c. Pollination and Fertilisation 



Pollination, as we have already learnt, is brought 

 about by the wind, which blows the light winged 

 pollen-grains in all directions, so that some of them 

 chance to alight on the female cones. This takes 

 place in May. Just before this happens, an interesting 

 change takes place in the female flowers, which pre- 

 pares them to receive the pollen. The axis of the 

 cone elongates a little throughout its whole length, so 

 that the ovuliferous scales are all shifted a little farther 

 apart. Thus an open space is left between each two 

 successive scales, through which the pollen-grains can 

 reach the ovules. 



At this time the ovule is still at an early stage of 

 development. The embryo-sac is still small, and is 

 not yet filled with prothallus. 



The integument opens widely, leaving an open 

 passage through the micropyle, leading down to the 

 apex of the nucellus. At the same time a small 

 quantity of liquid is secreted within the micropyle on 

 the surface of the nucellus. Some of the pollen - 

 grains carried by the wind pass between the ovuliferous 

 scales and come to rest on the edge of the integument 

 of an ovule. Another change now takes place: the 

 micropyle closes, the lips of the integument bending 

 inwards, and bringing the pollen -grains into contact 

 with the top of the nucellus, to which they adhere 

 owing to the liquid which has been secreted. 



The germination of the poll en -grain now begins. 

 Our Fig. Ill, j#, shows a pollen-grain, highly magnified, 



