164 BRITISH PLANTS 



the embryo-sac, discharges into it a nucleus, which fuses 

 with the nucleus of the egg-cell. The egg-cell, thus fer- 

 tilized, divides and develops into the new plant the 

 germ or embryo of the seed. The fusion of the male 

 cell with the egg constitutes the act of fertilization, and 

 by it the ovule becomes the seed. It is preceded by 

 pollination that is, by the transference of the pollen 

 from the stamens in which it is formed to the stigmas 

 upon which it germinates. After fertilization, great 

 changes take place in the ovules, a stream of food- 

 material pours into them, and their coats become modified 

 into protective envelopes for the seed. When these 

 changes are completed, water is withdrawn and the seed 

 passes into a resting or dormant state, from which 

 it only emerges at germination. 



The success of the seed, from the biological point of 

 view, is due to its efficiency in preserving the life of the 

 embryo during periods inhospitable to growth, and to 

 the ease and certainty of its dispersal by natural agencies. 



Pollination. 



The pollen which reaches the stigma comes either 

 from the same or from another flower. In the former 

 case the flower is said to be self-pollinated ; in the 

 latter, cross-pollinated. The terms " self- " and " cross- 

 fertilization " are often used in the same sense. This 

 is justified when pollination is followed by fertiliza- 

 tion, but when we are only concerned with the means 

 by which pollen is deposited on the stigma, and not what 

 happens to it afterwards, it is better to use the term 

 " pollination," reserving " fertilization " for the act of 

 sexual fusion itself. 



Self-Pollination (autogamy, Gr. autos, self ; gameo, I 

 marry). Autogamy is only possible when stamens and 

 pistil are both present in the same flower. The seeds so 

 produced give rise to offspring which more closely resemble 

 the parent than plants produced by the co-operation of 

 distinct parents. Self-fertilization is very common among 

 plants, even among those which seem specially adapted 

 for cross-pollination. On the publication of Charles Dar- 

 win's works on fertilization in flowers, people were so 

 struck with the wonderful adaptations among flowers for 



