Introduction

The phenomenon of guttation, like other physiological phenomena, is regulated by a number of internal and external factors. These factors mainly include the genetic makeup, growth and phenology of plants, hormonal and solute balance, temperature, humidity, light, and wind, which may conveniently be classified into the following heads and subheads.

Internal factors

These factors originate within the plants themselves and play a significant role in influencing guttation from leaves. These factors are briefly categorized and described below.

Genetic factors

Species variability

As stated earlier in Chapter 1, the phenomenon of guttation occurs in a wide range of plant species, which include herbaceous mesophytes, shrubs, and woody trees in angiosperms; gymnosperms; pteridophytes; algae; and fungi (Chen and Chen 2005; Lersten and Curtis 1991; Raleigh 1946a,b; Singh et al. 2009a; Sperry 1983; Stocking 1956a). Normally, significant guttation occurs in grass species including rice, wheat, barley, oats, and maize and other plant species such as tomato, balsam, Nasturtium, Colocasia, and Saxifraga and in some plants of Cucurbitaceae family as well; however, there is a high variability in guttate volume. Plants that exhibit guttation are seen to guttate through leaf tips, but in some plants, like the rice plant, guttation mainly occurs through the edges of the leaf, along with the surface, especially during the late hours of the day (Singh et al. 2008, 2009a). Few plant species exhibit profuse guttation under highly humid conditions, which appear as if water droplets are falling from the leaves (Feild et al. 2005). A single leaf of Colocasia antiquorum is capable of exuding up to 100–250 mL guttation water per day (Stocking 1956a). Guttation may also occur sometimes from the stems, generally through leaf scars or lenticels and flowers. The fungus Pilobolus is well known for its abundant guttation (Tarakanova et al. 1985; Tarakanova and Zholkevich 1986). Similarly, the fungus Polyporus squamosus also exudes droplets of water through its polypores profusely, which are similar to guttation in higher plants (Figure 1.2). Thus, these species of fungi, among others, present good examples of the occurrence of guttation.

As for guttation variabilities, it is worth mentioning that the exudation from Moso bamboo shoots during spring, in Southeast Queensland of Australia, can be sighted by the wet patches they create, having considerable agronomic and economic significance.