48 



STEMS 



4w 



61. Climbing and twining stems. 1 Since it is essential to the 

 health and rapid growth of most plants that they should have 

 free access to the sun and air, it is not strange that many should 

 resort to special devices for lifting themselves above their neigh- 

 bors. In tropical forests, where the darkness of the shade any- 

 where beneath the tree tops is so great that few flowering 

 plants can thrive in it, the climbing plants, or lianas (Fig. 39), 

 often run like great cables for hundreds of feet before they can 

 emerge into the sunshine above. In temperate climates no such 

 remarkable climbers are found, but many plants raise themselves 

 for considerable distances. The principal means by which they 



accomplish this result are : 



1. Producing roots at many points 

 along the stem above ground and 

 climbing on suitable objects by. means 

 of these, as in the English ivy (Fig. 14). 



2. Laying hold of objects by means 

 of tendrils or twining branches or leaf- 

 stalks, as shown in Figs. 40 and 41. 



3. Twining about any slender up- 

 right support, as shown in Fig. 42. 



4. Clambering upon bushes and 

 other supports by means of hooked 

 prickles, as is done by some roses, 

 blackberries, and cleavers (Galium). 



62. Tendril climbers. The plants 

 which climb by means of tendrils are 

 important subjects for study. Con- 

 tinued observation soon shows that 

 the tips of tendrils' sweep slowly about 

 in a circular or oval course until they come in contact with some 

 object around which they can coil. After the tendril lias taken 

 a few turns about its support, the free part of the tendril coils 

 into a spiral and thus draws the whole stem toward the point 

 1 See Kerner and Oliver, Natural History of Plants, Vol. I, p. 669. 



FIG. 40. Coiling of a tendril 

 of bryony 

 After Sachs 



