23 



of some plants, have the power of absorbing water. It 

 is not an uncommon practice to spray the leaves of plants 

 in the greenhouse when they are shaded, and alsojn the 

 open when the sun is no longer upon them and their sub- 

 sequent recovery, if they were drooping before, is attri- 

 buted to their having absorbed water. This is however 

 not the case. The spraying of the leaves, besides cooling 

 the foliage, which is often considerably heated by the sun, 

 has the effect by the evaporation of the water to render 

 the atmosphere around the plant moisture-laden, where- 

 fore the transpiration of the leaves is at once decreased. 

 It is this decrease of transpiration and not absorption by 

 the leaves which causes the revival of the plants. No 

 leaves with an impervious covering can take in water and 

 there are very few leaves which are not so protected. 

 Mosses and Filmy Ferns alone among leafy plants can 

 take in water through their leaves, which are adapted to 

 growth in moist if not dripping conditions. 



It is interesting to note that when the stomata are 

 closed and transpiration is impossible, some plants are still 

 able to get rid of their superfluous water. At night the 

 leaves of the Nasturtium and the Fuchsia for instance are 

 able to force out little drops of water through water-pores, 

 which are found at the termination of their veins. Many 

 grasses, too, have water-pores at the tips of their leaves, 

 and the drops of water exuded by them often look like the 

 formation of dew. 



When growing in very dry soil or in hot arid climes, 

 plants may experience a great difficulty in supplying their 

 leaves with water, often during a very prolonged period. 

 In such cases many remarkable deviations from the normal 

 structure are produced, with the object of -protecting the 

 leaves against drought. In most cases the leaves are small, 

 often reduced to mere scales or needle-shaped Structures. 

 Such are the leaves of many of our moorland plants grow- 

 ing in sanely, well-drained soil and exposed to strong and 

 drying winds. In still more arid regions the leaves may 

 disappear altogether, and we get such curious plants pro- 

 duced as the fleshy Cacti of the New World and the 

 succulent Euphorbias (Spurges) of the Old World. In 

 both of these groups of plants the green stems undertake 

 the process of assimilation, and they also store up sufficient 

 water during the wet season to enable the plant to last 

 out during a prolonged drought. 



