STEMS 



653 



family, fig. 958). Tendrils may be simple or forked and commonly 

 are sensitive to contact, coiling about their support ; in Sicyos the 

 sensitiveness is so great that the slightest friction incites differential 

 growth, resulting after a few moments in conspicuous curvature. 



The region of sensitiveness may be somewhat extensive, or (as in the pumpkin 

 family) confined to certain areas, known as tactile spots, where there may be thin 

 places or slight elevations in 

 the outer epidermal wall; the 

 tendrils that react most quickly 

 usually are those that have lo- 

 calized sensitive regions. Soon 

 after tendrils become attached 

 to a support, spiral coils appear 

 in the unattached portions (fig. 

 958), and the tendril-bearing 

 plant is drawn close to its sup- 

 port ; mechanical tissues also 

 may develop, increasing the 

 strength of the tendril (p. 699). 

 One of the most specialized of 

 tendrils is that of the Japan 

 ivy (Psedera tricuspidata) ; the 

 tendril branches terminate in 

 knobs, which upon contact 

 broaden out into disk-shaped 

 suckers that secrete a mucilagi- 

 nous substance and thereby ad- 

 here most tenaciously to walls 

 or bark (figs. 961-963). A 

 variety of the Virginia creeper 

 (Psedera- quinquefoUa) has 



FIG. 964. A fern (Nephrolepis) as a rhizome 

 climber on the palmetto (Sabal Palmetto); note that 

 the fern occurs at the upper part of the trunk where 

 the leaf bases persist; the rhizome dies below and 

 ascends pari passu with the developing palm ; Miami, 

 Fla. Photograph by E. W. COWLES. 



somewhat similar tendrils with 

 adhesive disks. 



Plants which climb by roots or 

 rhizomes. Root climbers have 

 been considered elsewhere, and 



it has been noted that anchoring roots, like tendrils, often are sensitive to mechanical 

 stimulation, and that such roots frequently grow horizontally about their support 

 > instead of growing downward as do most roots. Root climbers (as the English 

 ivy) are quite as able to adhere to vertical walls as are those plants whose ten- 

 drils have adhesive disks. The Virginia creeper sometimes climbs by roots as 

 well as by tendrils with adhesive disks. The elongating rhizomes of various 

 tropical ferns (as Nephrolepis) often come in contact with tree trunks, which 

 they may ascend, especially if the bark is spongy and easily penetrated (as in the 

 palmetto). If the rhizome continues to ascend, its ground connections may be 



