EQUISETINEAE. 



363 



longitudinal divisions ; it forms a ring of meristem (a thickening ring in Sanio's sense), 

 in which the vertical descending vascular bundles of the internode are formed ; these 

 bundles are the prolongation of the bundles of the teeth of the foliar sheath, which 

 they^meet at an obtuse angle (Fig. 216 g,g'}, and then coalesce with them to form 

 curved common bundles. The layers of cells outside this ring of meristem which 



FIG. 218. Equisetum arvense. Longitudinal section through the growing point of the stem ; sh leaf-sheath, st stem, 

 k rudiment of a bud. In the upper portion of the figure the apical cell of the bud has already formed some segments, 

 two of which are shown; in the lower portion the lateral bud is considerably developed and is overarched by the leaf- 

 sheath and the tissue of the stem st\ at -w is the rudiment of the root of the lateral bud. After Janczewski. 



forms the bundles produce the cortex of the internode, in which air-conducting inter- 

 cellular passages soon appear. The rudiments of the leaf-teeth (the teeth of the foliar 

 sheath) make their appearance at an early stage as protuberances at several 

 equidistant points on the apical line of the annular cushion, which forms a leaf- 

 sheath ; each of these protuberances ends in one or two apical cells (Fig. 2 1 7 *). 



1 On the original number and subsequent increase of the teeth of the sheath and on other points 

 see Hofmeister and Rees as cited on page 286. 



