Pollination and Fertilization I 59 



to enable the ovule to become a seed, or to form an embryo 

 within it, the pollen grain has to send out a little tube which 

 carries a marvellous body, the sperm cell or sperm nucleus. 

 Within the ovule there is another similar nucleus with which 

 the first must meet and unite. When this has been eflected 

 the ovule has been fertilized. Vou do not understand how 

 it is done ? Neither does an)' one else fully, but the process 

 can be seen by using a microscope, which you all may do 

 some day. 



It takes some time after pollination for fertihzation to take 

 place. It may be completed within a few hours. In the Arum 

 it takes several day-> for the pollen tube to reach the ovule 

 nucleus with its own, though the distance is so short. In Pines 

 the tube grows about half the length one year ; then it rests 

 through the summer and until about August of the following 

 winter and completes the journey by the beginning of November, 

 so that it takes a Pine cone two years to ripen. 



There are many devices used by flowers to prevent pollen 

 from coming in contact with the stigmas of the same flower, to 

 attract insects, and to ensure the pollen's delivery to its proper 

 destination — another flower of the same species.^ 



In early spring, Nature carpets the veld with Oxalis. Large 

 centre-pieces of brightest yellow are bordered with pink and 

 buff and white. The brighter the sun, the brighter will be the 

 carpet. Upon first sight the flowers appear to have fifteen 

 stamens. A second look will show five greener than the others, 

 tipped with round cushions that look as though they were stuck 

 full of pins. The cushions are stigmas. In some flowers they 

 stand higher than the stamens, in others shorter. Examine a 

 handful until you find some stigmas standing between the two 

 lengths of stamens. 



The Oxalis has a meaning when we know that bees which 

 visit it have long tongues, which are neatly rolled up when not 



' By prepotency of pollen is meant the power or quality by which 

 certain pollen fertilizes a given pistil in preference to other pollen. E.g. 

 the pollen of the same species is dominant or prepotent over the pollen of 

 another species. The pollen of another flower is prepotent over the 

 pollen of the same flower in Roella. 



