EQUISETINEAE. 



263 



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^,^'), and then coalesce with them to form 

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



I- IG. 218. Equisetnni arvense. Longitudinal section tlirough the growing point of the stem ; sh leaf-sheath, st stem, 

 /{• 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 -zi/ 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. 217 '). 



' On the original number and subsequent increase of the teetli of the sheath and on other points 

 see Hofmeister and Rees as cited on page 286. 



