THE STEM 



63 



stems of other phints for support (Fig. 38), and often 

 grow until tliey s[)read their own kM\es abo^'e tliose of the 

 phxnts that they encum- 

 ber. Tlie way in which 

 such climbers bend from 

 side to side until they 

 strike some vertical sup- 

 port may be told in tlie 



words of Darwin : — {^'7\''-!j')] n •"■''■ Twining stem of the 



Movniug Glory. 



" When the shoot of a lioji 



rises from the gvouiid, the two 



or three first-forineil joints. or 



interiiodes are straiglit and 



j-eniain stationary; but the next-formed, whilst very young, may be 



seen to bend to one side and to travel slowdy around towards all 



points of the compass, moving like the hands of a clock, with the sun. 



The nujvement very soon acijuires its full ordinary velocity. From 



seven observations made during August, ami on another plant during 



April, the average rate during hot weathei' and during tlie day is two 



hours eight minutes for each revolution ; and none of the revolutions 



varied much from this rate. The revolving movement continues as 



long as the plant continues to grow; but each separate internode, 



as it becomes old, ceases to move." 



74. The revolutions are less rapid at night than in the 

 (hij-time, but arc maintained until some object of sup]^>ort 

 is met with, when the free extremity still goes on revolv- 

 ing and the stem shortly encircles the support. The 

 movement then continues in an u[)«'ard-\Ainding spiral, 

 the coils tightening and the t\\'iner steadily ascending. 



75. Most spjecies of twining plants wind in a definite 

 direction. That is, as we hiolc down upon the plant, the 

 revolving tip moves with the hands of a watch lying face 

 upward, in some species ; opposite to the hands, in other 

 species. 



76. Another class of climbing plants includes those tliat 

 simply clamber in a haphazai'd fashion through and over 

 the surrounding herbage. The thorns of many IJrambles 

 and the minute backward-])ointing hooks studding the 

 ano'les of the stems antl the margins of the leaves in 



