12 



HOW PLANTS CLIMB. 



10. RoOt-CllmberS. These creep up the face of rocks or walls, or the trunks of 

 trees, their stems, as they grow, pressing against the support and adhering to it by 

 means of numerous rootlets which they throw out : the end of these rootlets com- 

 monly flattens out or expands into a small disk or holdfast which adheres to the 

 wall or bark, etc. Ivy, that is, true or "English" Ivy, is a good example of this. 

 See the vignette title-page, left-hand side. Our Poison Ivy and the Trumpet 

 Creeper climb in the same way. There is, perhaps, no .more eflFectual mode of 

 climbing when bare walls or large trunks are the support. In other cases 



11. Twiners, i. e. Twining Plants, have an obvious advantage. To twine spi- 

 rally round some supporting body is a common mode of climbing. This is 



done by a 

 movement 

 of the stem 

 itself, not 

 less re- 

 markable in reality than that of the leaflets of the Desmo- 

 dium gyrans, just described, and indeed of similar nature. 

 The Hop and some Honeysuckles twine with the sun. 

 Morning Glory, and all the Bindweeds of the Convolvulus 

 Family, Beans, and indeed most of the common twiners, 

 turn against the sun, that is, from the left to the right 

 hand of the observer. 



12. When a twining stem overtops its support, the 

 lengthening shoot is seen thrown over to one side, and 

 usually outstretched, as in Fig. 3. One might suppose it 

 had fallen over by its weight ; but it is not generally so. 

 If turned over, say to the north, when first observed, it will 

 probably be found reclining to the south an hour or so 

 later, and an hour later again turned northward. That is, 

 the end of the stem is sweeping round in a circle continu- 

 ally, like the hand of a clock. It keeps on growing as it 

 Fig. 3. Morning Glory, twining, revolves ; but the revolving has nothing to do with the 

 growth, and, indeed, is often so rapid that several complete sweeps may be made 

 before any increase in length could be observed. The time of revolving varies in 

 different species. It also depends upon the weather, being slow or imperceptible 



