Johann Baptista van Helmont (1577-1644) was a Belgian chemist and physician.

He was born in Brussels, obtained his medical degree from the University of Louvain, and returned to Brussels to practice medicine.

He moved later to Vilvorde and stayed there until his death.

His work on chemical research made him infamous to the Inquisition and he was imprisoned for two years (Rook 1964).

He started the inquiry which ultimately leads to the abandonment of the Humus Theory and to the understanding of the physiological process now called photosynthesis.

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Photoperiod, also called light duration and day length (or daylength), refers to the length of the light period as contrasted to the darkness within a day.

Day length controls or influences several plant growth and development processes that determine or affect crop yield.

The difference in day length can have a marked influence on the establishment and yield of certain crops.

As already mentioned, giant potatoes and cabbages have been produced in Alaska (about 61°N) during summer when light is intense and almost continuous.

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Seed plants or seed-bearing plants, also called spermatophytes or Spermatophyta, are vascular plants with numerous members belonging to the lignophytes or woody plants.

They have the natural ability to produce seeds, a characteristic that likewise distinguishes them from earlier plants.

The seed has been defined as an embryo surrounded by nutritive tissue and enveloped by a seed coat.

The embryo is an immature diploid sporophyte developing from the zygote (Simpson 2010).

Those which do not produce seeds are called seedless plants or non-seed plants.

They consist of both nonvascular and vascular plants and reproduce by means of spore.

The spore is defined by Simpson (2010) as a haploid cell that, in the land plants, originates from meiotic divisions of sporocytes within a sporangium, ultimately growing into a gametophyte.

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Enumerated below are the environmental factors affecting transpiration in plants.

These factors are described as “environmental” to distinguish them from those genetic factors which are inherent in the plants.

They are also described as external factors, that is, outside of or external to plants.

Specifically, they are climatic factors, that is, they are elements of the climate.

These factors are the same climatic factors that can either promote or inhibit plant growth and development and, eventually, crop productivity.

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C4 Photosynthesis. This mechanism of photosynthesis occurs in two adjoining types of cells, the mesophyll and bundle sheath cells in plant species called C4 plants.

Both C3 and C4 cycles operate in the non-light-requiring or Dark Reactions of photosynthesis but spatially, that is, in different cells: C4 in the mesophyll cells immediately followed by C3 cycle in the bundle sheath cells.

CO2 first enters the leaf and into the mesophyll cell.

It is then hydrated to produce bicarbonate ion (HCO3-) in the cytoplasm with carbonic anhydrase (CA) as catalyst.

This is the first step in C4 photosynthesis, followed by carboxylation reaction utilizing HCO3- instead of CO2 as the inorganic carbon substrate, Hatch and Burnell (1990) emphasized.

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