42 FUNDAMENTALS OF AGRICULTURE. 



to the bark adds to the bark on the inside. Each pe- 

 riod of growth of wood is marked as a ring, so that 

 in the temperate climates where the growth periods 

 are annual, the age of a tree can be quite accurately 

 determined by counting the rings in the cross section 

 of the trunk near the ground. 



Parts of Stems. A stem may be unbranched, as in 

 most palms, but usually is branched. At the end of 

 each branch is the growing point. This produces as 

 it grows, little projections on its sides which become 

 the leaves. At the point where a leaf joins the stem, 

 a bud is usually produced. It is by the growth of such 

 buds that branching of the stem occurs. Often they 

 do not grow unless the terminal bud is injured, in 

 which case they push out. 



EXERCISE. Bring in seed plants showing different kinds of roots. 

 Find as many different kinds of stems as possible. Bring in speci- 

 mens of leaves that are complete and that have certain parts lacking. 



SECTION IX. REPRODUCTION OF PLANTS. 



Flowers. When the plant has reached the proper 

 stage of development it prepares for seed production. 

 With the exception of the plants classed as Gymno- 

 sperms, which will be mentioned further on, this takes 

 place in special organs called flowers. 



Stamens and Pistils. The essential parts of flowers 

 are two; stamens and pistils. In the stamen is pro- 

 duced the pollen, a dust like usually yellowish powder 

 (more rarely a sticky mass of fine grain). This must 

 be brought in some way to the top of the pistil, where 

 each grain of pollen grows out into a microscopic tube 

 which bores its way down inside of the pistil, until 

 it reaches the minute bodies called ovules that are to 

 become the seeds. Entering one of these, the contents 

 of the pollen tube unite with its contents, and as a re- 

 sult of the union a new plant begins to grow. This 

 attains a certain size and then stops its growth, be- 



