NATURE OF PLANTS 93 



is led np 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. 68). The tip of these tendrils becomes greatly modified 

 so that they fit into every groove and crevice of the substratum. 

 Indeed in some vines these discs become so thoroughly cemented 

 to the crevices and irregularities of the support as to resemble 

 bits of melted wax. It is very interesting 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. 



46. 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 against 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 

 develops in this way and with the dying off of the old stem a 

 new plant is established, as in the houseleek (Fig. 69). In other 

 cases, runners, almost anv node mav form buds and roots which 



