Web Banner
Photo Unit 18 >


PHOTO UNIT 17: THE MONOCOT STEM

OBJECTIVES:

  1. Identify characteristics of monocot stems as distinguished from dicot stems.
  2. State the method by which secondary growth is accomplished in monocots.
  3. Identify primary thickening meristem in Yucca as seen in stem tip photos.
  4. Describe the vascular pattern and bundle composition in primary stems.
  5. Differentiate between primary and secondary bundles in Dracaena and describe the origin of each.

Photos for this study:

17-1: Acorus (sweet flag); Transverse section of rhizome

17-2: Triticum (wheat)' T.s. Eustele LP

17-3: Yucca (Spanish bayonet); Longitudinal section of stem tip

17-4: Yucca (Spanish bayonet); L.s lower down the stem apex

17-5: Dracaena (dracaena); T.s. stem primary bundle

17-6: Dracaena (dracaena); T.s. stem primary and secondary

17-7: Dracaena (dracaena); T.s. stem, early secondary bundle, HP

17-8: Dracaena (dracaena); T.s. stem, later secondary bundle HP

17-9: Dracaena (dracaena); T.s. secondary bundle HP


.

PHOTO STUDY 17-1: Acorus (sweet flag); Transverse section of rhizome.

Vascular bundles are disposed without apparent order here, just as you found them to be in Scirpus. They constitute a meristele, the type of stele you have come to expect in monocotyledon stems. But note that, in this stem, an endodermis is differentiated, marking the boundary between cortex and stele. Identify the very obvious Casparian strips in cells of the endodermis. Vascular bundles in the cortex are probably all leaf traces. Acorus, like Scirpus, is a plant living in marshy situations, which fact accounts for the numerous and large intercellular spaces in the ground tissue. Vascular bundles, as you noted in an earlier observation, are mostly amphivasal.


Back to top