232 THE LIFE OF THE PLANT 



plants we can still more easily be convinced of the 

 fusion of the substance of male and female cells. The 

 nature of this phenomenon, the chemistry of the process, 

 is almost unknown to us. A ferment has been dis- 

 covered among the constituents of the pollen grain, 

 and moreover during pollination increased chemical 

 activity is known to be generally displayed by flowers : 

 they greedily absorb oxygen and give off carbonic acid, 

 and this respiration is accompanied by a perceptible 

 rise in temperature of the whole flower, and especially 

 of the stamens. 



However, the result of this fusion manifests itself 

 in the awakening of formative activity in the embryonic 

 cell. It surrounds itself with a cellulose wall, becomes 

 divided by a partition, thus becoming two cells instead 

 of one (fig. 65, at the top, on the left). The first parti- 

 tion is followed by another, then by a third, and so on, 

 till a multicellular body is formed, which grows and 

 develops into the seedling which we met with in our 

 first lecture, in talking of the seed. Sometimes a 

 single seed has several embryos. This does not often 

 happen. There are several embryos in the seeds of 

 an orange, for instance, but they have quite a peculiar 

 origin, and it would be useless to enter here upon a 

 description of the process. Throughout the develop- 

 ment of the embryo stores of nutrient substances are 

 formed in other parts of the ovule, in the embryo-sac, 

 and in the nucellus ; this will be the part of the seed 

 which we have called the endosperm.^ The endo- 

 sperm being a store of food, it may either be absorbed 

 by the embryo while the seed is still on the maternal 

 plant, in which case the ripe seed will not contain any 

 endosperm, like the seeds of beans ; or, on the other 

 hand, most of the endosperm may be preserved in the 

 ripe seed, as in cereals, buck-wheat, the poppy, etc. 



The effects of fertilisation are not limited to the 



' See chapter iii. 



