8o 



OUTLINES OF PLANT LIFE. 



99. (/■) Tendrils. — Some shoots take the form of slender, 

 leafless, sensitive tendrils, which assist the plant in climbing 



by coiling about suitable objects 

 (fig. 69). 



100. {g) Thorns. — Many 

 plants produce defensive shoots, 

 which are leafless, rigid, short, 

 and sharp, called thorns, which 



Fig. 68. Fig. 69. 



Fig. ()%.—A , upper part of a plant of Polygonum •viviparum, showing flower cluster, 

 the flowers in lower half being replaced by tubers. Two-thirds natural size. B, a 

 fallen tuber. Magnifled about 3 diam. C, a plantlet growing from tuber. Natural 

 size. — After Kerner. 



Fig. 69. — A portion of the stem of white bryony, B, from which a tendril, w.r, arises 

 near the leaf stalk, ^, and the bud, k. «, rigid portion of tendril ; the portion between 

 « and the portion x, clasping the support, A , has become coiled into a spiral which 

 reverses the direction of the coils at w and w'. Nearly natural size.— After Sachs. 



may be either simple or branched (fig. 70). The honey- 

 locust furnishes an excellent example of branched, or com- 

 pound, thorns. 



