NATURE OF PLANTS 109 



brought into contact with branch after branch and thus the vine 

 is led up to the crown of the tree or to the top of the vegeta- 

 tion. The Virginia creeper, Boston or Japanese ivy, etc., have 

 peculiar tendrils that grow away from the light and form ad- 

 hesive discs, instead of coils, that bind the vine to the support 

 (Fig. 69). These discs are caused by the growth of the cells at 

 the tip of the tendril. As soon as the tendril hits the support 

 upon which the plant is growing, the cells at the tip are stimulated 

 to grow out and fit into every little irregularity and groove in 

 the substratum. Indeed in some vines these discs become in this 

 way so thoroughly cemented to the crevices and irregularities of 

 the support as to resemble bits of melted wax. It is very in- 

 teresting to watch the results of the stimulation induced by one 

 of these tendrils striking a wall or other support. The formation 

 and cementing of the disc are accomplished in about four days 

 in the case of the Virginia creeper. Some plants like the poison 

 and English ivy and many tropical plants climb by means of 

 roots. These organs, like the disc forming tendril, avoid the 

 light and seek the dark nooks and corners in the bark of trees or 

 rocks over which the plants grow. 



47. Prostrate and Creeping Stems. It is interesting to note 

 that a large number of plants having rather small and weak 

 stems like the climbers, have never acquired the habit of climb- 

 ing. The young shoots of these plants are often erect at first 

 but soon the weak stems bend over and become prostrate. While 

 these procumbent and creeping stems are at a disadvantage in 

 that they are obliged to arrange their leaves in one plane, on 

 the other hand they are not obliged to build up the elaborate 

 structures that are necessary for the support of the erect stems. 

 Consequently plants of this class are of common occurrence in 

 old fields and unfertile soils since they can subsist on a meager 

 supply of food. They are also protected agains.t injury and 

 therefore adapted to wind swept sandy plains, to rocky hills and 

 mountains, and to districts visited by heavy snows. The ma- 

 jority of these plants also have a very decided advantage owing 

 to the fact that certain nodes form roots and buds that develop 

 into new plants. In some cases, stolons, only the terminal bud 



