Light quality, also called spectral composition and spectral energy distribution (SED), refers to the composition of light as to wavelengths that are effective in photosynthesis and other plant growth and development processes. 

The wavelengths of light are expressed in small units of distance such as micron (μ) or micrometer (μm), nanometer (nm), and angstrom (Å).

One micron is one-millionth of a meter (10^-6 meter); 1 nanometer is one-billionth of a meter (10^-9 meter) or one one-thousandth of a micron, and 1 angstrom is one ten-billionth of a meter (10^-10 meter) or one ten-thousandth of a micron.

The wavelengths with primary importance in photobiology are ultraviolet (UV), visible light, and infrared (IR) (Hopkins 1999).

According to Devlin (1975), wavelengths between 300 nm to 900 nm are capable of affecting plant growth.

However, it is not light quality alone that affects plant growth processes.

Other properties of light including light intensity and light duration, as well as other climatic factors, are also involved.

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In broad terms, the stages of development in plants can be divided into the following: vegetative, reproductive, ripening, and senescence.

Each stage can be subdivided into various component substages or phases.

Although plant development is cyclical, here the seed is considered as the starting point for the sequential events leading to a mature plant, the formation of seed, and finally death.

The stages of development are listed hereunder in order of occurrence and should also provide at least a general picture of how plants grow from seeds until they die.

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Complete familiarity of the flower, flower parts, and their functions is necessary in understanding the subject of reproduction in the angiosperms or flowering plants.

It is particularly important in crop agriculture which includes the development of technology leading to increased yields in terms of flower, fruit, and seed.

The flower is unique to the angiosperms, from which all fruits and seeds develop.

It is the structure of the flower which became the basis of plant classification which Carl Linnaeus formulated and was to become the foundation of the science of plant taxonomy.

A flower is the plant reproductive organ of angiospermous plants which develops within a bud and consists of parts attached to the tip of a short modified stem called receptacle.

It is a determinate, modified shoot having either or both a stamen and pistil, with or without outer whorls of petals and sepals.

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Théodor Wilhelm Engelmann (1843 -1909) was a German botanist and physiologist.

He demonstrated that the site of photosynthesis is the chloroplast, the cytoplasmic organelle in plant cells which is responsible for the green coloration of leaves and other organs.

He also shed important enlightenment on the functions of light in photosynthesis, particularly light quality.

He showed that not all colors or wavelengths of light are effective in photosynthesis.

He therefore made significant addition to Ingenhousz’ finding that the degree of shade and brightness of the day (light intensity) affects the ability of plants to purify the air (photosynthesis).

It is now a well accepted fact that the process of photosynthesis is affected by the properties of light which include light quality, light intensity, and light duration.

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Soursop or guyabano trees (Annona muricata) can be grown using bare-root plants as planting materials, including wildlings.

Bare-roots are plants in which the roots are plainly visible, as in uprooted wildlings.

Wildlings are seedlings which naturally grow on forest floors or under the canopy of crops or just anywhere as when seeds are dispersed by man, animals, and water.

The term bare-root can also apply to nursery-grown potted seedlings and clones after removing the ball of soil holding the roots.

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In the angiosperms, self-pollination is the transfer of pollen from an anther to a stigma within one single plant.

It may occur within the same flower (intrafloral), or it may involve flower-to-flower (interfloral) pollen transfer within the same plant.

In contrast, cross-pollination is the transfer of pollen from an anther to a stigma in another flower in a separate plant.

The difference, therefore, is that the former occurs in one plant while the latter involves two plants.

However, any type of pollination may not be exclusive to a plant species.

One species may be classified as naturally selfing, but outcrossing can still occur in a few flowers or in some stigmas within the same flower or inflorescence.

There are various natural mechanisms in plants which promote either type of pollination. Some are briefly described here and on the next page.

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Julius von Sachs (1832 -1897). He was a German botanist and physiologist.

He achieved fame for his authorship of several books which have been translated to English and became standard textbooks in general botany and plant physiology.

He initiated experimental plant physiology and may be regarded as the pioneer in the conduct of studies on the physicochemical aspects of photosynthesis (Nickelsen 2007).

Reviewed by Govindjee and Krogmann (2004), Sachs showed that starch grains are produced in plant leaves and that these are the first visible product of the process of photosynthesis.

He also takes credit for proving that the green pigment chlorophyll in the chloroplast is involved in photosynthesis.

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2. Herbicide spraying – Three herbicides are commonly used to kill weeds in no-till corn farming: glyphosate, paraquat, and 2,4-D.

In general, the farmers in this part of Sarangani use glyphosate throughout the growing season.

However, under certain conditions, paraquat and 2,4-D are used as alternative or additive.

Glyphosate (N-(phosphonomethyl)glycine, ex. Roundup) is a nonselective, systemic (or translocated) post-emergence herbicide.

Being nonselective, it is a broad-spectrum herbicide capable of killing grasses, sedges, and broadleaved weeds except those genetically modified to resist or with natural tolerance to its toxicity.

It is ineffective on roundup-ready or glyphosate-resistant varieties of corn.

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Various terms are used to refer to the parts of leaves in angiospermous plants. These leaf parts are reviewed, including some modified parts in certain plants.

Parts of Leaves

A typical complete plant leaf consists of a broad, flat portion called blade or lamina, a leaf stalk or petiole which connects the blade to the stem, and a pair of stipules at the base of the petiole or at the nodes.

Stipules are outgrowth that may appear leaf-like, scale-like, or may even be represented by leaf sheaths or by spines.

Leaf sheaths are tubular structures at the base of certain leaves which clasp the stem, as in grasses.

In bananas, the erect pseudostem consists of overlapping leaf sheaths.

In most grasses, there is a thin appendage called ligule at the apex of the leaf sheath.

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