Stems, above-ground

Initially, farmers pulled out each plant out of the ground to get as much of the stem as possible. A farmer who uprooted his crop could clear a quarter of an acre per day. If he used a knife and cut the stems above ground, he could clear about a half acre. 

Experiment 1. Visual observation of secretory cells in luminescence microscope Various types of secretory cells in allelopathically active plants contain fluorescing secondary products (Fig. 1). Secretions from the above ground parts of plant (in leaves, flowers, stems) were concentrated in secretory hairs and glands. Whereas secretions of roots are in secretory reservoirs and idioblasts (ordinary cells which accumulate secretory products) or may be released by the secretory surface of the root tip (Fig. 1.). The fluorescence appears to change, when allelopathically active cell of other plant species (cell-donor) interacts with acceptor cell (Roshchina and Melnikova, 1999). 

Figure 7. DMSP inventory in S. altemiflora and above-ground biomass at four S. altemiflora sites in Great Marsh, Lewes, Delaware, in June, 1986. Most above ground DMSP is concentrated in live leaves although stems and dead leaves represent the majority of above-ground biomass at this time. Roots have less DMSP per unit biomass but may represent a larger pool on an aerial basis. Below-ground DMSP is less likely, however, to play a role in DMS emission as discussed by Dacey et al. (19).

There are two basic systems in a plant the shoot system, which includes above-ground elements such as leaves, stems, buds, and flowers and fruit (if there are any) and the root system, the underground parts, including roots, tubers, and rhizomes (Figure 4.1). 

Creeping perennials produce seeds but also produce rhizomes (below-ground stems), or stolons (above-ground stems that produce roots). Examples include johnsongrass, field bindweed, and Bermudagrass. 

The liverworts are one of three classes in the plant phylum Bryophyta. The other two classes are mosses and hornworts. Liverworts are small, green, terrestrial plants. They do not have true roots, stems, or leaves. Instead, they have an above ground leaf-like structure, known as a thallus, and an underground structure, known as a rhizoid. Most liverworts are found in moist environments and they tend to be less resistant to desiccation than their relatives, the mosses. Many liverwort species are found in temperate North America, but most species grow in the tropics. 

Radish (Raphanus sativus) is a plant that develops an underground, starchy, bulb-like structure in the tissue region known as the hypocotyl, occurring between the true roots and the above-ground stem. The familiar radish that is eaten is this inflated hypocotyl. The most commonly grown variety is a round, red radish with a... 

Figure 3 shows the spectra from measurement of a wheat stem sample with two different detectors, above ground and underground. It clearly shows the main advantage of using underground detectors for low level environmental samples. The peaks above the 1460 keV peak can be measured with very low detection limits. 

Figure 3 Gamma ray spectra from the same wheat sample (stem) measured in HADES and above ground at IRMM. The background spectrum from HADES is shown as comparison.

When the stem rises above ground and is apparent, the plant is said to be caulescent. 

Above-ground Stems.—funning stem winds around a support, as the stem of a beam or Morning Glory. 

Scale Leaves.—Scale leaves are reduced foliage leaves. They are found on certain rhizomes, above ground stems, such as Dodder, etc., on bulbs, and forming the protective scales of scaly buds. 

Fig. i86.—Podophyllum peltatum. Entire plant, above ground portion, and fruit. Note the flowering stems bearing in each instance two one-sided leaves and a nodding flower from the forks. This piant also sends up from its rhizome flowerless stems each of which terminates in a 7 -9 lobed peltate leaf. 

Unlike most other disease-eausing organisms, plant-parasitic nematodes seldom produce any characteristic symptoms. Most of the symptoms that do appear are vague and often resemble those caused by other factors, such as viruses, nutrient deficiencies, or air pollution. Nematodes feeding above ground may cause leaves, stems, and flowers to be tw istcd and distorted. 

The following abbreviations are used to indicate the plant part studied ag = above-ground parts fr = fruits 1 = leaves r = roots rh = rhizomes st = stems wp = whole plant... 

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