Page 16 - Medicinal Plants_PharmD general

3. Rainfall

For the proper development of plants, rainfall is required in proper
measurements. Xerophytic plants (a species of plant that has
adaptations to survive in an environment with little liquid water) like
aloes do not require irrigation or rainfall. The effects of rainfall on
plants must be considered in relation to the annual rainfall throughout
the year with the water holding properties of the soil. Variable results
have been reported for the production of constituents under different
conditions of rainfall. Excessive rainfall could cause a reduction in the
secondary metabolites due to leaching of water soluble substances
from the plants.

4. Day Length and Day Light

It has been proven that even the length of the day has an effect over
the metabolites production. The plants that are kept in long day
conditions may contain more or less amount of constituents when
compared to the plants kept in short day. For example, peppermint has
produced menthone, menthol and traces of menthofuran in long day
conditions and only menthofuran in short day condition. The day light
was found to increase the amount of alkaloids in belladonna,
stramonium, cinchona, etc. The development of plants varies
depending on both the amount and intensity of the light they require.
The wild grown plants adapt to the environment and grow when the
conditions are favourable but during cultivation we have to fulfil the
requirements of the plants.

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