4 MENDELISM CHAP. 



tential passage is left for the male cell. The majority of 

 flowers are hermaphrodite, and in many cases they are 

 also self-fertilising. The anthers burst and the contained 

 pollen grains are then shed upon the stigma. When this 

 happens, the pollen cell slips through a little hole in its 

 coat and bores its way down the pistil to reach an ovule 

 in the ovary. Complete fusion occurs, and the minute 

 embryo of a new plant immediately results. But for 

 some time it is incapable of leading a separate existence, 

 and, like the embryo mammal, it lives as a parasite upon 

 its parent. By the parent it is provided with a protective 

 wrapping, the seed coat, and beneath this the little em- 

 bryo swells until it reaches a certain size, when as a ripe 

 seed it severs its connection with the maternal organism. 

 It is important to realise that the seed of a plant is not a 

 sexual cell but a young individual which, except for the 

 coat that it wears, belongs entirely to the next generation. 

 It is with annual plants in some respects as with many 

 butterflies. During one summer they are initiated by the 

 union of two sexual cells and pass through certain stages 

 of larval development the butterfly as a caterpillar, 

 the plant as a parasite upon its mother. As the summer 

 draws to a close each passes into a resting-stage against 

 the winter cold the butterfly as a pupa arid the plant 

 as a seed, with the difference that while the caterpillar 

 provides its own coat, that of the plant is provided by its 

 mother. With the advent of spring both butterfly and 



