GUTTATION The process of exudation of liquid drops from the edges of leaves is called guttation. Usually it Occurs through stomata-like pores called hydathodes. Exudation may some times occur from stem through the scars of leaves and lenticeles. It is this process by which fully turgid plants remove extra water. The cause of guttation is mainly root pressure. Differences between transpiration and guttation are given in table
Hydathodes are stomata-like pores generally present at the tip or margins of leaves of those plants that grow in moist shady places (e.g., Tropaeolum). Pores are present over a mass of loosely arranged cells with large intercellular spaces called epithem This mass of tissue lies above a vein ending. The xylem of a small vein usually terminates among the thin walled parenchymatous cells of epithem. Due to root pressure water is forced out into intercellular space and flows out of hydathodes .
Amount of exudate may vary from few drops to many ml. Its quality may vary from pure water to dilute solution of organic and inorganic solutes containing aspartic acid, asparagine, several sugars and various other organic compounds. Guttation sometimes show endogenous rhythms. It ceases during the day and nearly always occurs at night. Mineral deficiency in plant may inhibit guttation.
Guttation is of less importance to plants. Sometimes it causes injury to the leaf margins by salt deposition which is left by evaporation of exudate. This creates favourable condition for the entrance of pathogenic organisms viz., fungi and bacteria etc.
Differences between transpiration and guttation
|1. Usually occurs in the day||1. Usually occurs in the night.|
|2. Water is given out inthe form of vapours||.2. Water is given out in the form of liquid.|
|3. Water vapours are pure||.3. Various dissolved sub- stances are present in guttation water.|
|.4. Occurs through stomata, lenticel or cuticle.||5. It is uncontrolled phenomenon|
|5. It is a controlled phenomenon.||5. It is uncontrolled phenomeno|
Expt. To demonstrate guttation.
A potted plant of garden nasturtium, glass plate, bell jar, aspirator, oil cloth, vaseline, thread.way
Place a small, well watered potted plant of garden nasturtium on a glass plate. Cover the open surface of soil with an oil cloth to avoid surface evaporation. Cover the plant with a bell jar. Close the mouth of bell jar with cork provided with a hole. Connect the hole by means of a glass tube to the aspirator. Make the apparatus air tight by smearing grease (or vaseline). Keep the apparatus for some time and observe.
Observation and Conclusions.
The drops of water appear on the margins (or vein endings) of leaves due to guttation.
Bleeding or Exudation
The term bleeding simply means a slow exudation of water sap from an incision when it is made in a plant tissue. For example, if an incision is made in the stem up to exlem, the xylem sap oozes out. In general,
four different types of bleedings are known-
(i) When an incision is made in the root or stem of well-watered young plant, the xylem sap oozes out due to root pressure,
(ii) Exudation of xylem sap due to local pressures developed within
stems. For example, if a 2 inches deep hole is drilled in the stem of sugar maple (Acer saccharum) tree, the xylem sap (solution of 2-3% sugars) exudates from the hole,
(iii) When the stems of palms, yuccas and agaves are cut, a phloem sap exudates due to local pressurein the stem, and
(iv) Exudation of milky latex from laticiferous ducts found in cortex and pith in the mem- bers of Euphorbiaceae when an incision is made to their plant tissues. The exudation of latex in the para rubber tree is the best example of this type. read more