After the pollen has been deposited upon 
the stigma each individual grain begins to 
expand, due to the food and the stimulus 
present in the sticky sugary substance on the 
stigma. Soon each grain sends out a tube 
called a pollen tube, which penetrates the 
top of the stigma and grows down through 
the style to the ovary, where it reaches the 
ovules shown in the diagram. It here pene¬ 
trates a very minute opening at the apex of 
the ovule, called the micropyle, and transfers 
a male nucleus into the egg cell within the 
ovule. The male sexual nucleus there unites 
with the female nucleus of the egg cell and 
completes the process of fertilization. From 
this union develops a cell containing proto¬ 
plasm, the nitrogenous living substance of 
which the most rapidly growing parts of 
plants are mainly composed. Each little 
ovule in which this pollination took place 
gradually develops into an apple seed. The 
