THE STEM AJSTD THE LEAF 



53 



are rapidly dividing to form neA\" ones, or, if not dividing, will 

 begin to do so whenever tliey are placed under favorable 

 conditions. Just back of the growing point ajjjiear little 

 protuberances (7) wliich are to develop into leaves. Further 

 along on the stem, each just forward of a rudimentary leaf, 

 are still more rudimentary branches (5j, b^, and so on). In 

 their youngest condition neither leases nor branches con- 

 tain any fibrovascular bundles, hut these soon appear, as 

 shciwn by the heaA'ily shaded areas in the figure. Once 

 equipped witli bundles for the trans[)ortation of \\ater and 

 food materials, the growth of the young branch into a stem 

 like that from which it sprang, ^\ ith bark, 

 wood, and pith of its o-\\-n, is comparatively 

 rapid. Branches of trees. Ijeing structur- 

 all}^ of the same nature as the stem, form 

 " annual rings," just as the main trunk 

 does. The wood of the branch cuts across 

 the "annual rings'" of the trunk and forms 

 a knot (Fig. 37 ).i 



50. Internal structure of the monocoty- 

 ledonous stem. In the very young mono- 

 cotyledon oiis stem of seedlings tlie fibro- 

 vascular bundles are ronstructed like those 

 of dicijtyledons, with the -wriod elements 

 on the one side and the cortical elements on 

 the other, as in Fig. 29. But in the full- 

 grown stems of most monocotyledons the 

 bundles have their vessels and other wood 

 elements arranged in a hollow cylinder „ „ ^ , . , 



11 "i.- 1 is, cut-off end of stick, 

 inclosmg that part of the bundle which showing annual rings : 



corresponds to the portion shown outside ^^' ^^°}' /ormed by 



^ , growth of a branch 



of the cambium rmg m Fig. 29. In the 



adult monocotyledonous stem (when it is solid) the bundles 



occur scattered all through the pith, as shown in a section of 



1 Knots may also be produced by injuries, but most of those found in 

 ordinary lumber were caused by branches. 



Fit. .37. Formation of 

 a knot in a tree trunk 



