514 



General Botany 



nuclei are discharged into the egg. One of the nuclei unites 

 with the egg nucleus; the other breaks down and disappears. 



Fig. 32 j. Sketch of a vertical section of a pine ovule and the scale to which 

 it is attached, showing male and female gametophytes at the time of fertilization : 

 pr is the prothallus with two archegonia ; in is the integument ; nu is the nucellus ; 

 m is the micropyle ; and ^ is a pollen tube, two of which have reached the neck 

 cells of the archegonia. (Redrawn from Strashurger.) 



The fertilized egg is the beginning of a new sporophyte genera- 

 tion, and its growth and development take place within and at 

 the expense of the food accumulated in the female gametophyte. 

 Two months after fertilization the young sporophyte, or embryo, 

 is fully formed and occupies the axis of the ovule. 



The seed. During the two years following pollination the 

 whole ovulate cone has been enlarging, and the ovules have 

 greatly increased in size. The integument has hardened into 

 a seed coat and the nucellus has been reduced to a membranous 

 layer inside it. Food has accumulated within the remaining 

 portion of the female gametophyte, usually called the endosperm. 

 The embryo has several cotyledons and a stem with growing 

 points at either end. The growing point which will ultimately 

 form the root is inclosed in a long sheath. 



In late autumn, or winter, the ovulate cone dies and its 

 tissues dry out; the sporophylls curl outward and the seeds 

 are liberated. As the seed separates from the sporophyll, a 



