14 THE LIFE HISTORY OF A TREE 



is entirely different, but need not be noticed here, as no 

 monocotyledon is of importance in British forestry. 



Running across the annual rings, on a section of oak, from 

 the centre of the tree to the bark, are seen some thin lines. 

 These are the medullary rays which cause the silver grain 

 when cut in a certain direction. They vary in breadth in the 

 different species, being difficult to see in coniferous timber. 

 Seasoning cracks usually follow these rays. 



The rays consist chiefly of soft cells, which keep up a 

 connexion through the harder timber from the pith (the 

 central part of the tree) to the bark, and they are used by 

 the tree, in addition to other parts, as store-houses for any 

 excess of starch, and are possibly concerned in the series of 

 changes whereby sap-wood is ultimately converted into heart- 

 wood. 



Reproduction. There is a natural provision for a future 

 generation by the means of seeds. All species have male 

 and female organs, though not necessarily on the same tree, 

 the seeds being produced by the females after fertilization by 

 the males. These reproductive organs are called flowers, 

 whether conspicuous or not. To understand the structure of 

 a flower it is as well to examine a simple one like that of a 

 buttercup. On the under-side of a buttercup we find five 

 greenish-yellow floral leaves ; these are the sepals, whose duty 

 it is to protect the inner parts of the flower while in the bud 

 stage. The five sepals together are called the calyx. Inside 

 these we find five bright yellow petals, and, if one is examined 

 carefully, a small honey gland or nectary will be found at 

 the base of the upper surface. These petals, which are to- 

 gether called the corolla, serve to attract insects Within these 

 petals we find a large number of stalked stamens, each of 

 which has a yellow swollen head. This head, which is called 

 the anther, contains a very large number of yellow grains 

 called pollen grains, each of which contains the male fertilizing 

 substance. The stamens are therefore sometimes called the 



