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Dicot stem
Monocot stem
Broad pith
Weak stem
Monocot fiber sheaths
Ordinary cortex
Aerenchyma hypodermis
Aerenchyma cortex
Aerenchyma cortex 2
Stem endodermis
Palisade cortex
Cortical bundle
Capped cortical bundles
Collapsible cortex
Perimedullary fibers
Conjunctive tissue, paren.
Torn pith
Hollow pith
Medullary bundles
Typical dicot bundle
Vascular ring
Typical monocot bundle
Amphivasal bundle
Corn vascular bundle
Clintonia bundles
Protoxylem
Metaxylem
Metaxylem parenchyma
Metaxylem fibers
Internal phloem
Internal phloem, mag
Developing metaxylem
Primary phloem
Phloem fiber cap
Developing fibers

Fig. 11.4-2. Transverse section of corn stem (Zea mays). The vascular bundles of monocots stems typically occurs in a complex three dimensional pattern embedded in a matrix that is called conjunctive tissue. Conjunctive tissue may be either parenchyma as in this corn, or it can consist of fibers whose walls can become extremely thick. As you might imagine, parenchymatous conjunctive tissue occurs in monocot stems that are soft – such as corn, canna lilies, gingers, and bulbs like onions – whereas a fibrous conjunctive tissue occurs in larger, harder monocot stems like bamboo, agaves, and many species of palm trees.

            In this micrograph, we can see eight vascular bundles, but if we could somehow make the conjunctive tissue perfectly transparent so that we could see far down into this stem, almost certainly we would see that some of them come together and join to be a singe bundle, others might branch into two and so on, such that they form an interconnected network, not just a set of bundles each isolated from the others.