CMG GardenNotes #133 Plant Structures: Stems

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1 CMG GardenNtes #133 Plant Structures: Stems Outline: Functins, page 1 Structure, page 2 Internal features, page 2 Mnct r Dict, page 2 External features, page 3 Types f stems, page 5 Mdified stems, page 6 Thught questins: (Explain the science behind the questins.) My trees have been severely drught stressed fr the past few years. Why are they still shwing stress when we had gd misture this year? Over the winter, rabbits girdled my tree all the way arund dwn t the wd. My neighbr said it wuld die, but it leafed ut nicely. Will it be OK? I planted several new trees ver the past few years. Hw can I evaluate hw they are grwing? Hw can I tell if rts are established s I can begin structural pruning? Stems are the part f a plant that bear leaves and flwers, and they are the cntinuatin f the vascular system pipeline that starts in the rts. Functins Framewrk fr leaves, flwers and seeds Cntinuatin f vascular system carrying water and minerals frm the sil, and sugars manufactured in leaves thrughut the plant. Green stems als manufacture fd. Fd strage Hrticultural uses Aesthetic (winter interest in the landscape, appealing bark, etc.) Feed and fd Fuel Plant identificatin Prpagatin (cuttings and layering) Wildlife habitat Wd industry and cnstructin 133-1

2 Cmmn Types f Stems Wdy Plants Sht First year grwth n a wdy r herbaceus plant. Twig Wdy stem less than ne year ld. Branch Wdy stem mre than ne year ld. Trunk Main supprt stem(s) f wdy plants. Water spruts Juvenile adventitius shts arising n a branch. Generally very rapid, upright-grwth, and prly attached t the main limb. Suckers Juvenile adventitius shts arising frm the rts, generally rapid, upright-grwing. Canes Stems with relatively large pith and usually living fr nly ne t tw years (rses, grapes, blackberries, and raspberries). Structure Internal Features Apical meristem Tissues at the tip f a stem capable f cell divisin, gives rise t stem elngatin. Epidermis Outer layer f wax-cated cells that prvides prtectin and cvering Crtex Primary tissues f a stem externally bund by the epidermis and internally by the phlem. Vascular bundle Phlem tissues (inner bark) distribute sugars (prducts f phtsynthesis) thrughut the plant. It is imprtant t understand what happens when the phlem is blcked, as when a tree is girdled with a tie r rpe. The stem ften enlarges just abve the blckage due t the sugars mving dwn frm the leaves fr distributin thrughut the plant. Tissues belw the blckage slwly starve. Rts die back, eventually leading t death f the plant. Cambium tissues are the single-celled layer f meristematic (dividing) tissues that cntinually divides t frm phlem tissues tward the utside and xylem tissues tward the inside. Cell divisin f the cambium tissues adds width t the stem. Xylem tissues Distribute water and minerals frm the rts up thrugh the plant. Xylem prvides the structural supprt in plants, becming the wdy tissue. Pith Center f dict plant stems. In sme plants the pith breaks dwn frming a hllw stem. In lder wdy plants, the pith is filled with rigid xylem wd fiber. Figure 1. Crss sectin f stem Wdy dict stems are used in tree and shrub identificatin. Features t lk at include the crss sectin shape f the pith (runded, star, r triangular) and whether the pith is slid, hllw, r chambered

3 Figure 2. Stem pith is used in plant identificatin. It may be slid, hllw r chambered. In a crss sectin, the pith may be runded, triangular r star shaped. Tree Rings In wdy dict plants, the rings grw t make a cmplete ring arund the stem. Xylem grwth makes the annual rings used t tell a tree s age. In wdy dict plants, water and mineral mvement ccurs in the mre recent years f xylem rings. Drught reduces the size f the annual rings (size f xylem tubes) and thus the ptential fr water and nutrient mvement. Multi-year drughts, with their crrespnding reductin in xylem size, have lng-term impacts n plant grwth ptential. [Figure 3] Figure 3. Crss sectin f herbaceus (left) and wdy (right) dict stems External Features Bud A stem's primary grwing pint. Buds can be either leaf buds (vegetative) r flwer buds (reprductive). These buds can be very similar in appearance, but flwer buds tend t be plumper than leaf buds. Terminal bud Bud at the tip f a stem. In many plants, auxin (a plant hrmne) released frm the terminal bud suppresses develpment f lateral buds, thereby fcusing the grwth f the plant upward rather than utward. If the terminal bud is remved during pruning (r natural events) the lateral buds will develp and the stem becmes bushy. [Figure 5] Figure 5. External features f a stem Lateral buds grw frm the leaf axils n the side f a stem. Leaf scar Mark left n stem where leaf was attached. Often used in wdy plant identificatin

4 Bundle scar Marks left in the leaf scar frm the vascular tissue attachment. Used in wdy plant identificatin. Lenticel Pres that allw fr gas exchange Terminal bud scale scars r annual grwth rings Marks left n stem frm the terminal bud scales in previus years. Terminal bud scale scars are an external measure f annual grwth. Therefre, they are imprtant in assessing plant vigr. [Figure 6] Figure 6. Terminal bud scars r annual grwth rings Nde Segment f stem where leaves and lateral buds are attached. [Figure 7] Nte: Rts d nt have ndes. Internde Sectin f a stem between tw ndes Bark Prtective uter tissue that develps with age. Used in wdy plant identificatin. Figure 7. Nde and internde Bud type The type f bud is als used in plant identificatin. Figure 8 illustrates bud types used in the Manual f Wdy Landscape Plants. [Figure 8] All the features previusly described can tell a great deal abut a plant pertinent t its identificatin and health. These are cmmn terms that frequently appear in literature

5 Figure 8. Bud types Mdified Stems Bulb Thickened, undergrund stem with fleshy strage leaves attached at base (tulips, lilies, nins). Crm Shrt, thickened, undergrund stem with reduced scaly leaves (gladilus). Crwn Cmpressed stem having leaves and flwers grwing abve and rts beneath (strawberry plant, dandelin, African vilet). Stln (r runner) Hrizntal, abve-grund stems ften frming rts and/r plantlets at their tips r ndes (strawberry runners, spider plants). Rhizme Hrizntal, undergrund stem, typically frms rts and plantlets at tips r ndes (iris, bentgrass, cannas)

6 Spur Very cmpressed, fruiting twig fund n sme apples, pears, cherries and ginkg. Twining stems Mdified stems used fr climbing. Sme twist clckwise (hps, hneysuckle); thers twist cunterclckwise (ple beans, Dutchman s pipe). Tuber Enlarged rhizme cntaining stred fd. (Irish ptat; the eyes f the ptat are mdified buds.) Tuberus stem Shrt, flattened, mdified strage stem (tuberus begnias, dahlias). Unlike tubers, which have buds scattered all ver, tuberus stems nly have leaf buds n the "up" end. Authrs: David Whiting, Cnsumer Hrticulture Specialist (retired), Clrad State University Extensin; with Michael Rll and Larry Vickerman (frmer CSU Extensin emplyees). Line drawings by Sctt Jhnsn and David Whiting. Revised by Patti O Neal, Rberta Tlan and Mary Small, CSU Extensin. Clrad Master Gardener GardenNtes are available nline at Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised June