372 ELEMENTS OF GENERAL SCIENCE 



grows down through the stigma and style into the ovule 

 and so reaches the vicinity of the egg. While the pollen 

 tube has been growing down into the ovule two male cells 

 have developed within it. One of these may unite with the 

 egg cell, thus producing the fertilized egg. Each male cell 

 is capable of fertilizing the egg hi the ovule. 



382. The embryo plant. After fertilization the egg of the 

 plant like the egg of the frog proceeds at once to grow. 

 Through cell division and enlarge- 

 ment one region develops into the 

 root tip, another into the stem tip, 

 and others into one or more leaves. 

 In most cases, when the young plant 

 has developed these different regions, 

 the wall of the ovule becomes hard- 

 ened and the embryo becomes dor- 

 mant. This is the mature seed. It 

 may lie dormant for a short or a long 

 period and then grow. 



383. The seedling. When seeds of 

 plants are placed in favorable situa- 

 tions moisture is absorbed by the 

 young plantlet inclosed within the 

 seed coats, and its growth is soon 



continued. The seed coats are burst ; 

 FIG. 1<4. A peanut seedling . , 



the root tip emerges and grows into 



the earth and develops additional roots. The way in which 

 the young stem and leaves (fig. 174) emerge from the seed 

 coats is extremely variable. In the seed of the bean there 

 is an elongation of the stem of the young plant This elon- 

 gated stem bends in such a way as to pull the leaves out of 

 the seed coats. In other cases, as in the sunflower, the leaves 

 grow upright and push the seed coat into the air, dropping 

 it only after the leaves have become well separated from one 

 another. When the young plant has become well established 



