144 



BOTANY 



Plants living in water have loose and 

 spongy tissues ; many large intercellu- 

 lar spaces are found in stems or leaves. 

 In one pond lily (Nelumbo lutea) these 

 spaces in the leaf communicate with 

 large spaces in the veins of the leaf, and 

 these in turn with spaces in the petiole, 

 stem, and root, so that all parts of the 

 plants are in communication with the 

 air above. The roots of a plant living 

 wholly in water are not needed for sup- 

 port, hence they arc often short and 

 stumpy. They do not need to be 

 modified to absorb water ; consequently 

 the absorbing surface lacks root hairs. 

 The whole plant, when under water, is 

 usually modified to take water (and 

 with it food) from its immediate en- 

 vironment. 



Hydrophytes. — If water is pres- 

 ent in such quantity as to satu- 

 rate the soil in which the plant 

 lives the conditions of its en- 

 vironment are said to be hydrophytic and such plant is said to 

 be a hydrophyte. 



Xerophytes. — The opposite 

 of hydrophytic conditions is 

 seen when the soil is very dry. 

 Such a condition is known as 

 xerophytic, and the plants liv- 

 ing in these conditions are 

 xerophytes. Such is the con- 

 dition in a desert. We have 

 seen that the most important 

 adaptations of xerophytes are 

 such as prevent evaporation 

 of water from their bodies. 

 The leaf surface is reduced, 

 the leaves being changed into 

 spines as in the cactus, or very 

 greatly reduced in size, as in 

 the switch plants of our alkali 



A water plant, showing the finely divided 

 leaflike pax'ts. 



Plants with floating leaves. 



