12.1: Primary Growth
- Page ID
- 35376
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Tissues in the shoot are derived from the shoot apical meristem (SAM). Just like in the root, the SAM produces three primary meristems, which produce the primary tissues:
- Protoderm → Epidermis
- Ground meristem → Cortex and pith (simply ground tissue in monocots)
- Procambium → Primary xylem and primary phloem
These primary tissues will then either differentiate into specialized cells or, as is the case in many eudicots, become meristematic and produce secondary tissues.
Coleus Stem Tip
Though it looks a bit alien, this is a section through a growing tip of a plant. In the center, where the alien’s head might be, is a region of small, densely packed cells. This is the SAM of the apical bud. On either side of the SAM, like two upraised arms, are the leaf primordia. These are the early stages of developing leaves. Through the center of these leaf primordia is a darker region of small cells. This is the procambium, which will develop into the vascular tissue. Lining the outer edge of the SAM and the youngest portions of the leaf primordia is the protoderm. As the protoderm matures into the epidermis, it produces hair-like projections called trichomes. Between the protoderm and the procambium is the ground meristem.
On either side of the growing tip are two other darkened lumps of densely packed cells. These bud primordia will develop into axillary buds, producing either branches or flowers. Each bud primordium has its own SAM.
![Partial view of a Coleus shoot tip long section](https://bio.libretexts.org/@api/deki/files/27403/Coleus_stem_tip.jpg?revision=1&size=bestfit&width=721&height=542)
![A closer view of the Coleus stem tip](https://bio.libretexts.org/@api/deki/files/27404/Coleus_stem_tip_tissues.jpg?revision=1&size=bestfit&width=639&height=481)
Monocots
Figure \(\PageIndex{3}\): A cross section of a Zea mays stem. The organization of tissues differs from the Zea mays root. Most notably, the vascular tissue is arranged in bundles, rather than a central cylinder. These bundles are densely packed toward the outside of the stem, then occur less frequently toward the inside. Because there is no distinct delineation of the tissues produced by the ground meristem, it is now called ground tissue (as opposed to cortex and/or pith). Photo by Maria Morrow, CC BY-NC.
![A closer view of the corn stem cross section](https://bio.libretexts.org/@api/deki/files/27409/Zea_mays_stem_tissues.jpg?revision=2&size=bestfit&width=654&height=492)
![Zea mays stomata and closed vascular bundles](https://bio.libretexts.org/@api/deki/files/27410/Zea_mays_stomata_near_bundles.jpg?revision=2&size=bestfit&width=612&height=460)
Eudicots
Helianthus
![A cross section of a Helianthus stem](https://bio.libretexts.org/@api/deki/files/27414/IMG_20200610_113721.jpg?revision=2&size=bestfit&width=562&height=651)
![Helianthus young stem vascular bundles, cortex, and epidermis](https://bio.libretexts.org/@api/deki/files/27415/Helianthus_young_stem_vascular_bundles.jpg?revision=2&size=bestfit&width=622&height=468)