48 NATURE TEACHING 



the presence of fine lines well seen in a rose stem 

 running through the wood, joining up pith and cambium. 

 They are also well indicated by radiating cracks, often 

 formed in posts or felled timber which has been exposed 

 to the weather for some time. These are the medullary 

 rays which serve to connect up and maintain com- 

 munication between the various parts. 



If now a stem of maize, cane, or almost any other 

 monocotyledonous plant is examined, the parts will be 

 seen to be arranged in a very different manner from 

 those of the stems already studied. In the stems of 

 this second set we can distinguish no pith, no ring or 

 column of wood, no separable bark, and no cambium. 

 They exhibit in cross-section a groundwork of soft 

 tissue, in which harder portions are irregularly scattered ; 

 and whilst the outer portion forms a kind of rind, it is 

 not essentially different from the rest, but merely con- 

 tains a much greater proportion of the hard portions, 

 and very little of the soft ground-tissue. On cutting 

 such a stem lengthwise, it is readily seen that the hard 

 portions are in reality fibrous strands which run through 

 the stem. 



For a full description of the various tissues compos- 

 ing these two types of stems, the reader is referred to 

 botanical text-books. 



Grafting and Budding. 



The existence of the cambium in the stems of dicotyle- 

 donous plants renders possible the carrying out of certain 

 operations known as grafting and budding. This 

 depends upon the fact that the cambium, being a region 



