Holm: Juncus repens Michx. 3G3 



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. and somewhat more Compressed than the otlier. The outer cell- 

 wall of epidermis is slightly thickened and the cells are sometimes 

 developed as bulliform, especially outside the lacuncs. The bark- 

 parenchyma contains chlorophyll and consists of palisades. Simi- 

 lar to the leaf the mechanical tissue is poorly represented in the 

 stem and occurs only as small groups on both faces of the mes- 

 tome-bundles, but without being in contact with epidermis, and 

 without forming any closed ring around the inner part of the stem. 

 The mestome-bundles, the large and small ones, form only one 

 peripheral band and their structure corresponds exactly to that of 

 the leaf-bundles. There is a starch-bearing pith, which occupies 

 the inner part of the stem ; it is, together with the bark, interrupted 

 by lacunes, which are somewhat larger in the prostrate, than In the 

 erect, flower-bearing stem. This structure of the stem does not 

 seem different from that of other species of Juncus, examined so 

 far, with the exception of the arrangement of the mestome-bundles 

 in two nearly parallel planes on account of the compressed outline. 

 In the cylindric stems the mestome-bundles lie in one concentric 

 band, and the pith occupies the Innermost part of the central 

 cylinder, interrupted by a single or several concentric lacunes. 



As very little is known of the root-structure in North Amer- 

 ican Juncaceae, we might state, that there Is a persisting hypoderm 

 of only one stratum and that the bark-parench}-ma collapses radi- 

 ally with the exception of the innermost two layers, which border 

 on the endodermis. The inner cell-walls of endodermis are very 

 much thickened (Plate 363, Fig. 6) and show a number of layers. 

 The pericambium is thin-walled and very regularly interrupted by 

 the proto-hadrome vessels, there being Invariably only two peri- 

 cambium-cclls outside the leptome. A large vessel occupies the 

 center of the root, and is surrounded by two strata of thick-walled 

 conjunctive-tissue. The interruption of the pericambium by the rays 

 of the hadrome, the proto-hadrome vessels, is a character which the 

 Juncaceae, at least a number of species, have In common with sev- 

 eral genera of Gramineae, Cyperaceae, Centrolepldeae, etc. Besides 

 this the presence of a mestome-sheath is anotlicr character which 

 is known to occur in all the Cyperaceae examined, but not in all 

 the Gramineae; according to Schwendencr it has not been ob- 

 served In any of the Andropogoncae or Maydeae, or in several 

 genera of Paniccae. Considered from an anatomical view point 



