229 



others. Similarly the fact that the Cocoanut tree (Cocos nucifera) 

 in nature usually occurs on the saline soil of the seashore 

 formerly led to the belief that the tree required a large quantity 

 of salt in the soil. The fact that this tree grows well in gardens 

 on ordinary soil, however, disproves this, and we are driven to the 

 conclusion that the tree can only thrive m nature on saline soils 

 owing to the fact that, in such localities, the majority of other 

 plants cannot exist, and that it is driven out of more favour- 

 able localities by stronger competitors. 



208. Another important point p ower O f 



concerning plant distribution is the fact that most plants possess Adaptation 

 a considerable power of adapting themselves to a new environ- * ^itff 1 " 611 * 

 ment, to changed conditions of existence. We very often hear, 

 for instance, of plants which have become acclimatised. Some 

 species possess this power in a high degree, others are less adapt- 

 able. It must be remembered that a plant which thus adapts 

 itself to new conditions undergoes a more or less fundamental 

 change, acquires as it were a somewhat different constitution, 

 and this may, or may not, be manifested by an obvious change 

 in its outward form, or habit. We have already seen, in Part V 

 above, that certain individuals of one and the same fungus 

 nourished by different hosts may differ essentially from one 

 another although they cannot be distinguished by any visible 

 character, see page 199. This undoubtedly also occurs in higher 

 plants, but in many cases also remarkable changes are notice- 

 able, some of which have been already mentioned under varia- 

 tions in Part IV above, see pages 152 155. In some cases 

 plants show the change they have undergone by flowering 

 and leafing at different periods of the year, or by becoming 

 more or less deciduous, or evergreen. 



209. A plant which is adapted to Xerophytes. 



thrive in a locality where very little water is available is termed ^^ and 

 a xerophyte. Such plants are usually provided with a large and T - ( pophytes. 

 well developed root-system and with devices for preventing 

 excessive loss of moisture by transpiration. Thus they fre- 

 quently have small leaves (the transpiring surface being thus 

 reduced), which are coriaceous, or fleshy, with a thick-walled 

 epidermis, and often provided with a protecting covering of 

 hairs, etc. They also often possess water-storing tissue. They 

 are often provided with thorns, or spines, and sometimes with 

 mobile leaflets which close up in strong sunlight. Hygrophytes, 

 on the other hand, are plants adapted to thrive in a locality 

 where an abundance of water is always available. They are 

 usually provided with contrivances for accelerating trans- 



