STEM FORMS AND USES 



143 



elld), respectively. Prostrate and trailing stems are very 



apt to become creepers by the development of adventitious 



roots at their nodes, 



wherever they come 



in contact with the 



soil. Between the 



extremes of prostrate 



and upright, stems 



may be in various 



degrees, 



Assurgent, that is, 

 ascending, like com- 

 mon crab grass and 

 spotted spurge {Eu- 

 phorbia maculatd), or. 



Declined zxvd droop- 

 ing, as the garden jessamine, the matrimony vine {Lycium), 

 and some of the garden spireas. The most interesting of 

 all in their mode of growth are the various forms of 



-Prostrate stem of Lycopodium with 

 assurgent branches. 



203. Twining and Climbing Stems. — The former rise from 

 the ground by twisting themselves spirally round their sup- 

 port, like the morning-glory, hop, 

 and yellow jessamine ; the latter 

 by attaching themselves to other 

 objects by means of adventitious 

 roots and tendrils, as the Virginia 

 creeper, poison ivy, pea, grape, 

 smilax, etc. A curious fact about 

 twiners is that with one or two 

 exceptions each species always 

 coils uniformly in the same direc- 

 tion and can not be made to 

 change. Raise a young hop or 

 morning-glory plant in the school- 

 room, notice whether it starts to 

 coil from right to left or from left 

 to right, and see if you can coax it to grow in the opposite 



236 287 



286, 287. — Twining stems : 



286, hop twining with the sun ; 



287, convolvulus twining against 

 the sun. 



