Pollination and Fertilization 125 



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 most marvellous little body called a nucleus. 

 Within the ovule there is another similar nucleus with which 

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

 the ovule has been fertilized. You do not understand how 

 it is done ? Neither does any one else yet, but it can all be 

 seen and drawn by using a microscope, which you all may do 

 some day. 



It takes some time after pollination for fertilization to take 

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

 it takes several days 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 

 over winter and makes the rest of the journey the following 

 year, so that it takes a pine cone two years to ripen. 



There are thousands of 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 ,. . — ',.^f^ ■— — __Z ^r" 



when not in use. When a 



...-,, Fig. 139. — Diagram of bee's tongue after 



flower IS visited, the tongue visiting Oxalis with long and short stamens. 



is uncoiled and thrust down 



the flower after honey. If the bee has just visited a flow^er 



with lon^ and short stamens, there will be tell-tale marks on 



