THE NEW FIELD BOTANY. loi 



have only needle-shaped leaves or even no true ones at all, as many 

 of the cacti in the desert lands of the Western plains. 



Again, the surface of the plant may become covered with a felt 

 of fine hairs to prevent rapid evaporation, while other plants with 

 ordinary foliage have the acquired power of moving the leaves so 

 that they will expose their surfaces broadside to the sun, or con- 

 trariwise the edges only, as heat and light intensity determine. 



Phytoecology deals with all those adaptations of structure, and 

 from which permit the plants to take advantage of the habits and 

 wants of animals. If we are studying the vegetation of a bog, and 

 note the adaptation of the hydrophytic plants, the chances are that 

 attention will soon be called to colorations and structures that in- 

 dicate a more complete and far-reaching adjustment than simply 

 to the conditions of the wet, spongy bog. A plant may be met 

 with having the leaves in the form of flasks or pitchers, and more 

 or less filled with water. These strange leaves are conspicuously 

 purplish, and this adds to their attractiveness. The upper por- 

 tion may be variegated, resembling a flower and for the same pur- 

 pose — namely, to attract insects that find within the pitchers a 

 food which is sought at the risk of life. Many of the entrapped 

 creatures never escape, and yield up their life for the support of 

 that of the captor. Again, the mossy bog may glisten in the sun, 

 and thousands of sundew plants with their pink leaves are growing 

 upon the surface. Each leaf is covered with adhesive stalked 

 glands, and insects lured to and caught by them are devoured by 

 this insectivorous vegetation. 



In the pools in the same lowland there may be an abundance 

 of the bladderwort, a floating plant with flowers upon long stalks 

 that raise them into the air and sunshine. With the leaves reduced 

 to a mere framework that bears innumerable bladders, water ani- 

 mals of small size are captured in vast numbers and provide a large 

 part of the nourishment required by the highly specialized hydro- 

 phyte. 



These are but everyday instances of adaptation between plants 

 and animals for- the purpose of nutrition, the adjustment of form 

 being more particularly upon the Vegetative side. Zoologists may 

 be able to show, however, that certain species of animals are 

 adapted to and quite dependent upon the carnivorous plants. 



An ecological problem has been worked out along the above 

 line to a larger extent than generally supposed. If we should take 

 the case of ants only in their relation to structural adaptations 

 for them in plants, it would be seen that fully three thousand spe- 

 cies of the latter make use of ants for purposes of protection. The 

 large fighting ants of the tropics, when provided with nectar, food, 



