STEMS 



235 



its fastened extremities naturally results in two spiral 

 coils running in opposite directions. In this way the 

 stem is fastened to its support by numerous spiral springs. 

 All of these movements and their results may be observed 

 by cultivating a plant such as the star-cucumber, which 

 grows rapidly and has conspicuous and very sensitive ten- 

 drils (Fig. 201). In the case of the ordinary climbing 



FIG. 203. Woodbine in a deciduous forest. 



woodbine and certain species of ivy, which cling to walls 

 or tree trunks, the tip of the tendril when it comes in contact 

 with a support is stimulated into developing the disk-like 

 sucker which acts as a holdfast (Fig. 202). 



133. Stem-structure. There are two general types of 

 stem-structure exhibited by Seed-plants, one belonging to 

 the Gymnosperms and Dicotyledons, and the other to the 

 Monocotyledons. Since the latter is only a modification 

 of the former, the stem of a Dicotyledon will be used as an 

 illustration. 



