Young herbaceous dicot stem

In some species, gas exchange

In a dicot stem, the vascular tissue is not in the centre, but in a ring of columns around the outside. The micrograph below shows part of a typical dicot stem.

The centre of the stem is occupied by a very light tissue called pith, consisting of air spaces and large, thin-walled cells. The pith is virtually "empty", and thus adds little weight to the stem.

The ring of columns provides much greater structural stability than a solid stem would. (The Egyptians and Greeks discovered this in their temple building periods, but dicots beat them to it by about 65 million years!).

The outer layer of the stem is called the epidermis. Unlike the epidermis in a young root, it must be waterproof, so it secretes a waxy cuticle to keep water inside the plant. Note that relative humidity is high, temperature is low, and wind is non-existent in the soil, so water loss through roots will be low, but the opposite is true above ground. Without adequate waterproofing, a plant would rapidly dry out.

Inside the cuticle is a layer of cortex made mainly of thin walled parenchyma cells. In most plants, these contain many chloroplasts and carry out photosynthesis. In very young plants, photosynthesis by the stem can provide quite a significant part of the plant�s food. Note that photosynthesis requires exchange of carbon dioxide and oxygen with the air. Tiny pores called stomata allow gases to pass through the cuticle and epidermis. Guard cells surround the stomata, and can close the pores if water loss becomes severe. The cuticle will rarely be thick, as the cells would shade one another.

Each column is called a vascular bundle and is adapted for transportation and support. The micrograph below shows a vascular bundle. The epidermis is toward the top right (not visible).

In many plants, there will be a ring of very thick-walled cells called fibres surrounding the bundle. In small herbaceous plants these are usually live collenchyma cells, while in larger herbs and woody plants they are further thickened and hardened into non-living sclerenchyma cells.


Many phases of propagation

2009-07-01 10:34:10 by AnitaMoPlants

You were correct in eliminating some of the leaf surface and making a shallow wound in the base of the stem.
For soft wood stem cuttings one usually makes a clean cut just below a node in the stem and then a one inch sliced wound .
You may not have lost the plant. Roots may form this autumn.
The leaves may have fallen from drying out or perhaps a fungus formed in the soil
With evergreen leaf cuttings I sometimes will put plastic over the cuttings to keep the humidity up .
Environmental control such as stress, too much water, not enough light or a soil fungus appearance are all plausible reasons for the leaf drop


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DALY: Use care when planting around septic drainfields  — Gwinnettdailypost.com
Shallow rooted annual and perennial herbaceous plants can be planted closer to the drain fields since they do not have invasive roots. Turfgrass can be grown over the drain field and is beneficial since it helps hold the soil in place.

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