lecture 15, stems and leaves Flashcards
how are adventitious roots helpful in maize plants?
contribute to N-fixation and bracing. bracing limits horizontal and vertical plant movement. also likely important for the uptake of water and nutrients
what is the pith?
ground tissue in the center of monocot roots
what kind of stele is present in dicots?
protostele
no pith in the middle of dicot roots
what kind of stele is present in monocots?
eustele
what is the Shoot?
- plant structure that produces leaves and axillary buds (shoot apex)
- contains nodes and internodes. at each node, strands of vascular cylinder turn outward
what are the primary tissues of the stem?
apical meristem containing:
- leaf primordia: develops into leaves
-bud primordia: develops into lateral shoots
how is the shoot apical meristem organized?
Tunica-corpus:
- the tunica divide anticlinically (outwards)
- the corpus divides periclinically (parallel) and add bulk to the growing shoot
what does the central zone of tunica-corpus contain?
corpus and parts of the tunica. central zone is surrounded by peripheral zone a very mitotically active site
what does the apical meristem of the shoot contain?
- protoderm
- arises from outermost tunica (L1) layer - procambium
- peripheral zone (emanating most from corpus) - ground meristem
- corpus
what are the 3 basic types of stem structure?
- vascular system, continuous cylinder within ground tissue
- cylinder of discrete bundles separated by ground tissue
- vascular bundles that are spread throughout - ground tissue cannot be distinguished between pith and cortex (common amongst monocots)
characteristics of continuous cylinder (type 1)
a vascular cylinder with an almost continuous ring, separated by imperceptible interfascicular regions.
the outer cells are the primary phloem and the inner cells are the primary xylem, results from procambium division.
contains a single layer of undifferentiated cells that turn into the vascular cambium and then into secondary phloem/xylem
what are the characteristics of Discrete Strands (type 2)
contain interfascicular regions that consist of pith rays. pith rays separate pith and cortex.
secondary growth in type 2 is partly fascicular and partly interfascicular
what do procambial strands do?
give rise to primary xylem and phloem (sieve elements)
significance of type 2 discrete stranded in some herbaceous dicots:
- retain no procambium after primary tissue mature
- vascular bundles are closed
- no vascular cambium
characteristics of type 3 scattered:
- monocots - vascular bundles scattered throughout the ground tissue
- procambial strands: phloem develops from outer cells, xylem from inner
