INTERNAL S'liaCTlHK OK STKMS. 



41 



109. BulbletS are little Imlhs, or tlcshy hutls, t'oriucd in llio axils of leaves al)ovo 

 grouiid, as in the liullj-bearinjir Lily. Or in some Leeks and Onions they take 

 the place of (lower-bnds. Fallintf ofF, they take root and grow into new plants. 



no. The Internal Structure of Stems. rUuts are conipo.sed of two kitids of 



material, namely, Crllular Tixxiw and WhdiI. The former makes the softci-, 

 fleshy, !ind pithy parts ; the latter forms the harder, librous, or woody parts. 

 The stems of herbs contain little wood, and mucii celhdar tissue; those of 

 shrubs and trees abound in the woody part. 



III. There .are two great classes of stems, which difTer in the way the woody 

 part is arranged in the cellular tissue. 'I'hey are named the JUo'jciious and the 

 A'7iif6>/ef/nn>t. 



1 1 2. For examples of the first class we may take a Bean-stalk, a stem of Flax, 

 Sunflower, or the like, among herbs, and for woody stems any common stick 

 of wood. For examples of the second class take an Asparagus-shoot or a Corn- 

 stalk, and in trees a Pidm-stem. These names express 

 the difTerent wavs in which the two kinds grow in thickncs.s 

 when they live more than one year. But the difference 

 between the two is almost as apparent the first year, and 

 in <he stems of hei*bs, which la.st only one year. 



113. The Endogenous Stem. Kudixfuoui^ means "inside- 

 growing." Fig. 77 shows an Eiidogenous stem in a Corn- 

 stalk, both in a cross-section, at the top, and also split 

 down lengthwise. The peculiarity is that the wood is all 

 in separate threads or bundles of fibres running lengthwise, 

 and scattered among the cellular tissue throughout the 

 whole thicknes.s of the stem. On the cross-section their 

 cut ends appear as so many dots ; in the slice lengthwise 

 they show themselves to be threads or fibres of wood. 

 Fig. 78 is a similar view of a Palm-.stem (namely, of our 

 Carolina Palmetto, of which whole trees are iH'[)rcsonted 

 in Fig. 79). It shows the endogenous plan in a stem 

 several years old. Here the bundles of wood are merely 

 increased very much in number, new threads having been 

 formed throughout intermixed with the old, and any in- 

 crease in diameter that has taken place is from a general distention or enlarge- 



78 

 Endogenous Stems, 



