THE LIFE HISTORY OF A TREE 15 



male organs of the plant. In the very centre of the flower 

 we find a large number of small bottle-shaped carpels, which 

 together form the pistil As the carpels of the buttercup are 

 very small it is best to examine a young pea-pod which is 

 a single carpel of the pea-plant in a rather later stage ; it will 

 be seen that the carpel is a hollow body containing ovules 

 which after fertilization grow and become seeds. The carpel 

 is therefore, on the analogy of the stamen, the female organ. 

 The hollow part of the carpel is called the ovary. At the 

 outer end of the carpel we find a thin projection with its end 

 feathery. This feathery portion is called the stigma, and the 

 stalk-like projection from the ovary is called the style. The 

 carpel thus consists of the ovary which bears ovules ; the 

 stigma which is feathery or sticky and which catches and 

 holds the pollen grains ; and the style which holds the stigma 

 in position, connects the ovary with it. and provides for the 

 passage of pollen tubes to the ovules. In some plants several 

 carpels are joined together to form a single ovary ; in this 

 case there are often as many separate stigmas as there are 

 carpels in the united ovary. 



The pollen from a ripe stamen is carried by insects from 

 flower to flower and in course of time it touches a ripe stigma, 

 to which it sticks. The pollen grain then throws out a tube 

 which grows down the style into the ovary and finally reaches 

 an ovule into which the contents of the pollen tube are emptied. 

 Fertilization is thus completed and the ovule now grows into 

 a seed and the ovary into a fruit. 



The flowers of trees vary in many details from that of a 

 buttercup, but the general process of fertilization is similar. 

 In some cases the pollen is blown about by the wind, and is 

 not carried by an insect. In this case the flower often has no 

 petals, and is frequently inconspicuous. Some trees (e. g. lime) 

 have both stamens and pistils in one flower. Others (e. g. hazel 

 and oak) have them in different flowers on the same tree; 

 in the hazel the familiar catkins are a collection of male flowers 



