176 MORE ABOUT STARTING NEW PLANTS 



II. NON-SEXUAL PROPAGATION: PARTS OF THE 

 PLANT CONCERNED 



To understaud better the non-sexual propagation of plants it is 

 necessary to know more about their stems, roots, buds, and leaves, 

 the parts by which they are propagated. 



125. Stems. Most farm plants have one or the other of 

 two kinds of stem. One kind is illustrated by the pear 

 tree ; the other, by corn. 



a. An examination of a stem of a pear tree 1 will show 

 three distinct groups of tissue in it: the bark; the cambium; 

 and the wood. 



(1) In the bark, especially in the bark of new stems, 

 numerous openings may be seen, about as large as ordinary 

 pinheads. These are breathing pores for the deeper layers 

 of bark. The bark serves mainly to protect this next group 

 of very tender, liquid-like tissue. 



(2) This middle group of tissue, between bark and wood, 

 is the cambium. From the viewpoint of growth and re- 

 production, it is the vital part of the stem. Its cells contain 

 protoplasm in a more active form than in those of any 

 other part of the stem; and some of this is germ plasm and 

 may create a new plant. 



There are two layers of cambium cells: one adhering 

 to the inside bark; the other, to the outside wood. The 

 two together are about as thick as a leaf of the paper in 

 this book. A boy often sees the two cambium layers of 

 the willow when making willow whistles in the spring. 

 After hammering the bark to loosen it, he pulls it away 

 from tt piece of the stem; then sometimes he scrapes away 

 loose, moist particles that cover the surface of the wood. 

 These particles are the inside layer of cambium. Perhaps 



1 Surh an examination can be made most easily in the spring when sap is 

 starting. 



