NATURE'S WOODCRAFT: A CHAPTER ON STEMS 



221 



joint). Holocyclic articulation is characteristic of monocotyledons. The 

 mericyclic stem differs materially from the holocyclic, the stem-joints or 

 internodes being arranged side by side (juxtaposed) as well as superposed ; 

 and therefore occupy only a portion of the diameter. Thus, in the case 

 of leaves arranged spirally on a stem, the internode is only a segment of 

 the diameter extending from one leaf to that which comes exactly above or 

 below it. This arrangement of leaves is made clear in the next chapter, 

 but for our present purpose it may be said that according to the number 

 of leaves in one complete turn of the spiral round the stem, so there is 



Photo by] 



FIG. 276. WOOD-SORREL (Oxalis acetosella). 



IE. Step. 



The plant is sensitive to atmospheric changes. The leaflets fold down close to the leaf-stalk at night and on the 

 approach of rain. A slight jar of the leaf-stalk will produce the same effect. If a plant is put into a dark 

 cupboard the leaflets will assume the nocturnal pose, and if then brought out into full daylight will spread out at once. 



a corresponding number of segments or internodes juxtaposed in its 

 diameter, and all beginning on different levels. When the leaves form 

 a whorl, as in the Bedstraws (Gcdium) and Woodruff (Asperula), there 

 will be as many internodes as leaves, but all beginning and ending at 

 the same level. We cannot go into all the details here ; but we may say 

 in brief that whereas the former theory of Braun and Sachs regarded the 

 stem as a pre-existing basis on which the leaf is developed, Celakovsky 

 holds with Fleischer and Hegelmaier that the leaf is first formed and 

 develops from its base a Stengelglied or internode. 



A hollow and unbranched stem, the intern odes of which are separated 



