Page:The Oak.djvu/83

 As a rule, the outer and inner side of these bast groups are in contact with vertical rows of nearly cubical parenchyma cells, strongly thickened on the side next the bast, and each nearly filled with a crystalline clump or with an imperfectly formed crystal of oxalate of lime. Similar vertical rows of crystal cells may also occur within the groups of bast fibers, the walls of the cubical cells being more or less thickened and simply pitted. Occasionally a cell here and there retains thin walls. The vertical rows result from cross-divisions of prosenchymatous mother-cells, the conical ends being found in macerations.

Within the groups of bast fibers are yet other rows, similarly formed, of parenchyma (Fig. 17, bp), the cells of which are longer, however, attaining the length of the wood-parenchyma; like the latter also their walls are lignified and rather thick, and they contain starch in the winter. Thus we have parenchyma in the bast. Transitions between these two forms of parenchyma cells are also found.

The cells of the rays between the bast fibers are thickened and pitted; they are rounded, and not in vertical series as in the rest of the rays, but are scattered in no particular order. Sometimes they are few, and one or all with very thick walls perforated by pit-canals (Fig. 17, bs).

The remaining younger part of the bast consists chiefly of delicate, apparently irregular parenchyma cells with cellulose walls; this is easily traced to the