Minnesota Plant Life. 435 



may be seen in plants of northern regions. If leaves are ex- 

 posed to a heavy rainfall the surfaces are often lacquered or 

 waxy, and, by means of the coating-, rain is diverted and there 

 can be little danger of the tissues becoming v^ater-logged. 

 Upon such leaves grooves or furrows may be developed. 

 Through these the water is quickly drained and is not allowed 

 to accumulate. Slender points are distinctive of leaves upon 

 which too much moisture accumulates for the good of the 

 plant, and especially in tropical forests are these rain-tips, as 

 they are called, ordinary characters of the leaf. It has even been 

 shown that trees growing in the spray of waterfalls develop 

 leaves slightly different in shape from the ordinary leaves of 

 the species and marked both by furrows on the upper side 

 and by elongated tips. Because of the danger of rain or dews 

 clogging the air pores of leaves these tiny apertures are in most 

 instances assembled on the lower surfaces of leaves, where 

 they are protected. Or, if they occur on the upper surfaces 

 there are hairs, or pegs of cell wall substance, or blooms of wax 

 or shellac, which guard them and make it difificult for them 

 to be wet. Such protections against moisture are particularly 

 common in fiowers, where it is essential that the pollen should 

 be kept dry. The shapes of the petals, the positions of the 

 stamens, and a variety of other adaptations make the wetting 

 of pollen by rain improbable. Many fruits are furnished with 

 blooms of wax or with hairs by means of which they easily 

 shed water. No such contrivances are to be looked for in the 

 root system, or on the leaves or stems of submerged plants. 

 In water-lily leaves and other floating varieties, where the air 

 pores are all upon the upper surface of the leaf, decidedly waxy 

 coatings are often developed to keep the water from the 

 pores. In some varieties, as, for instance, the oleander, the 

 pores open into special chambers or depressions, on the under 

 sides of the leaves, and the mouths of these are guarded by 

 "non-wettable" hairs, thus affording absolute protection to the 

 air pores. Many of the different positions, shapes and textures 

 of leaves and flowers are to be ascribed to such adaptations 

 against unfavorable moistening. 



The root tract of plants, which in most instances is the spe- 

 cial absorptive area, is fitted by structure and position for the 

 work it has to do. The young roots are furnished with in- 



