IN ANGIOSPERMAE. XEROPHILOUS PLANTS 



165 



The question we may now ask is do these primary leaves exhibit 

 a form of leaf which has arisen through adaptation to life in water, or do 

 they not? Whilst there can be no doubt that there is a connexion 

 between the number of these leaves and the mode of life of the plants to 

 which they belong, yet the fact that in a large majority of other 

 monocotyledonous plants the band- 

 like form of leaf is typical and that 

 these leaves are able to adapt themselves 

 to a land-life, taken along with other 

 circumstances, led me early to the view 

 that there is no sufficient foundation 

 for the assumption conveyed in the first 

 part of the above question. 



The submerged primary leaves in some 

 dicotyledonous plants also have a simpler 

 construction than, and present a configura- 

 tion different from those which appear above 

 the water. In Fig. 100 a seedling of the 

 nymphaeaceous Victoria regia is represented 

 upon which the first floating leaf d, which 

 differs from those following it, has been 

 already formed ; the three preceding leaves 

 are submerged ones, and in a the leaf-blade 

 is not yet marked off from the stalk ; in 

 b and c its configuration is different from 

 that of d. We have here to do with peculiarly 



developed arrested formations, and this is shown by the fact that the shoots formed 

 upon tubers of Nymphaea rubra bear primary leaves like those of the seedling, 

 and that under unfavourable conditions of growth, such as, for example, very deep 

 water, Nuphar luteum remains for a long time at the stage at which water-leaves are 

 formed similar to those produced in germination. 



FlG. loo. Victoria regia. Seedling plant. The 

 leaves are lettered in the order of their succession, 

 .y seed-coat; /? chief root; j; r\, r^ lateral roots. 

 After Trecul. - 



C. XEROPHILOUS PLANTS. 



Plants of this description live in localities where they are at times 

 exposed to the danger of too great transpiration, and they frequently 

 possess, as is well known, adaptations to their habitat l which are ex- 

 pressed chiefly in diminution of the size of the leaf or in the formation of 

 leaves with a vertically expanded lamina, as in Eucalyptus, and in the 

 phyllodes of Acacia. When the shoot-axis of xerophilous plants has to do 

 the work of assimilation instead of the leaves, it is usually broadened out. 



1 So conspicuous are these that they have in recent years been described ad nauseam. 



