Theory:

What is excretion in plants?
Excretion is a catabolic process in which the toxic and waste products are eliminated from the body of an organism.
Unlike animals, plants lack a well developed, advanced and specialized excretory system. They are devoid of excretory organs. Thus, excretion in plants is not so complex.
The excretory products of plants:
Plants, like animals, indulge in metabolic activities like cellular respiration, photosynthesis, and other metabolic responses that result in excretory products.
 
The two gaseous waste products of plants are carbon dioxide produced during cellular respiration and oxygen produced during photosynthesis.
 
These wastes are excreted through the pores of the stomata on the leaves. Photosynthesis uses the oxygen released during photosynthesis for respiration, while photosynthesis uses the carbon dioxide released during respiration.
Transpiration:
The excess water in the plants is also excreted from the plant body through the stomatal pores and from the surfaces of fruits and stems. The process of elimination of water is called transpiration.
The loss of water in the form of water vapour from the aerial parts of the plant body is known as transpiration
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Transpiration
 
The leaves of green plants have tiny, microscopic pores known as stomata. The water content in the plants evaporates through these stomata.
 
Structure of stomata:
  
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Opening and closing of stomata

Each stomatal pore is surrounded by two kidney-shaped cells known as guard cells that help in regulating the rate of transpiration by opening and closing of stomata.
Types of transpiration:
Transpiration is of three types based on the site where they occur. They are as follows:
  1. Stomata transpiration
  2. Lenticular transpiration
  3. Cuticular transpiration

1. Stomatal transpiration:

The loss of water from the plants through stomata is known as stomatal transpiration. \(90-95%\) of the water that is transpired from the leaves occurs through the stomata.

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Stomatal transpiration
 
2. Lenticular transpiration:
What are lenticels?
The tiny openings that protrude from the barks in woody stems and twigs and other plant organs are known as lenticels.
When compared to the stomata, lenticels are less in number.
 
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Lenticular transpiration
  
The loss of water from the plants through the lenticels is known as lenticular transpiration.
  
3. Cuticular transpiration:
 
It is a transpiration that takes place from the surface of the leaves. The leaves are covered by a waxy layer known as the cuticle, which helps in reducing the amount of transpiration taking place.
The loss of water from this cuticle is known as cuticular transpiration.
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Cuticular transpiration
Need for transpiration:
  • It is a process that creates a water pull (movement of water from the roots to stem and leaves)in the leaf and stem.
  • It creates an absorption force in the roots.
  • It is required for the continuous supply of minerals.
  • As it is involved in the loss of water, it is also involved in the regulation of the temperature of the plant.
A video explaining the process and types of transpiration with an experiment:
Other waste products of plants:
Apart from gaseous wastes, plant metabolism produces organic by-products such as gums, oils, latex, resins held in old xylem, barks (ancient phloem cells), stems, leaves, and other materials that plants shed due to the presence of dead cells.
 
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Resin on the bark of a tree
  
Plants also excrete some waste substances into the soil around them.
Reference:
https://commons.wikimedia.org/wiki/File:Figure_30_02_05abc.jpg
https://www.flickr.com/photos/visionshare/4500284946
https://commons.wikimedia.org/wiki/File:Opening_and_Closing_of_Stoma.svg
https://commons.wikimedia.org/wiki/File:Kale2.jpg
https://www.freepik.com/free-vector/diagram-showing-transpiration-plants_5916230.htm
https://www.freepik.com/free-vector/diagram-showing-transpirationplant_6078279.htm#page=1&query=transpiration%20in%20plants&position=1
https://commons.wikimedia.org/wiki/File:Cherry_tree_resin.jpg