CHAPTER XVI 



POLLINATION AND FERTILISATION 



Flowering Plants. There is one feature in which all 

 flowering plants differ from non-flowering plants that is, the 

 production of seeds. They are often spoken of as seed plants 

 in contradistinction to seedless plants. If certain conditions 

 are fulfilled, the ovules become changed into seeds. There is 

 no other way in which seeds can be produced, except by 

 changes in the ovules which convert them into seeds. The 

 ovules of to-day become the seeds of to-morrow, and the seeds 

 of to-morrow form the plants of the future. 



The conditions which are necessary for the conversion of an 

 ovule into a seed are as follows : 



(1) The pollen gram formed in the anther must find its way 

 on to the stigma of the pistil. This transference of the pollen 

 from the andrcecium to the gyncecium is called pollination. 



(2) The pollen grain must germinate and form a pollen tube, 

 which must grow down the style and enter the micropyle of the 

 ovule. The generative nucleus of the pollen grain must be set 

 at liberty and unite with the oosphere in the embryo-sac. The 

 union of the generative nucleus of the pollen grain with the 

 oosphere is called fertilisation. 



(3) The oosphere after fertilisation is called an oospore or 

 egg-spore, an( i must develop into an embryo or young plant 

 (P- ii). 



(4) Food materials must be removed from the leaves of the 

 plant into the embryo-sac, there to be used up by the developing 

 embryo during its early growth, or to be stored until the 

 germination of the seed takes place, 



