20 THE STORY OF PLANT LIFE 



male cell divides into two. The pollen-tube going 

 down the stigma and style penetrates the micropyle 

 and passes into the ovule ready to fertilise the egg-cell. 



Turning to the maturation of the embryo-sac, 

 in the middle of the ovule is the nucellus enclosed in 

 two (or a single) integuments, except at the micro- 

 pylar end. The ovule and the integumentary tissue 

 unite below in the chalaza. When all are in a straight 

 line the ovule is orthotropous. If the micropyle lies 

 close to the funicle or stalk of the ovule it is ana- 

 tropous, and campylotropous when the nucellus and 

 integuments are bent over laterally. 



In the nucellus when the megaspore has matured 

 the embryo-sac is developed near the upper end. 

 The nucleus divides into two, and one cell goes to 

 each pole. They divide into four, one of each 

 returning to the centre to form the secondary nucleus, 

 replacing the first. It has thus eight cells which 

 are formed by the division of the nucleus. 



The lower three cells are the antipodal cells. The 

 upper three are the egg apparatus, consisting of two 

 synergidae and the ovum or egg-cell. 



When fertilisation is about to take place, the male 

 cell fuses with the ovum, and as a result of this, or 

 fertilisation, the embryo is formed. One male gene- 

 rative cell fuses with the egg-cell. The ovum or 

 egg-cell divides and grows and develops into the 

 embryo. The ovule with the ovum and the integu- 

 ments thus becomes a seed. 



As regards the development of the embryo, the 



