176 



EDWARD C. JEFFREY ON 



region of the rhizome of E. silvaticum. The branch, as in the other cases, originates 

 from the lower region of the nodal wood. 



From all these examples it will be sufficiently obvious that in Equisetum the 

 branches arise neither above nor below the nodal wood but from it, and in the case 

 of the smaller branches, from its lower border, and in that of the larger ones, more 

 or less exactly from its central region. In E. limosum at the subterranean nodes, 

 whether of upright or horizontal stems, there are present one or two branch-buds 

 and a number of rhizophorous buds. From the latter as many as six or seven roots 

 grow out into the soil, and the stem-region of the buds more or less completely 

 degenerates. That these root-bearing pedicels are the morphological equivalents of 

 branches is obvious for two reasons : in the first place they possess a typical medulla 

 like the shoot-organs, and are thus distinguished from the pithless roots which are 

 characteristic of the modern Equiseta ; secondly, by examining the successive nodes 

 of an upright branch, beginning below the soil and passing upwards, it is possible to 

 distinguish all phases of transition between rhizophoric organs and typical leafy shoots 

 These results are only confirmatory of those of Janczewski (Recherches sur le dev. des 

 bourgeons dans les preles. Mem. soc. nat. sci. Cherbourg, 1876, torn. 20), but it is impor- 

 tant to have independent evidence in these matters as will appear in the sequel. 



It has already been stated that the leaf-traces originate from the protoxylem of the 

 bundles of the lower internode. Photograph 4 (PI. 30, fig. 4) demonstrates the accuracy 

 of this statement. The leaf-trace is separated rather widely from the surface of the nodal 

 wood, and the endodermis forms a deep bay on the outer side of the node, between it and 

 the leaf-trace, as is represented in PI. 26, fig. 14. 



Before leaving this part of the subject one interesting feature may be referred to. 

 Photograph 5 (PI. 30, fig. 5) represents a section of the nodal diaphragm of E. hiemale. 

 It is easy to make out that the cells of the upper portion of the diaphragm are arranged 

 in perpendicular rows, and that the lower members of the rows have become thick-walled, 

 forming the characteristic sclerification of the diaphragm. These features are of con- 

 siderable interest, because peridermal tissue has been recently described as occurring 

 in the diaphragms of Calamites by Williamson and Scott (Phil, trans, roy. soc, 1894, B., 

 p. 889). In the Calamites, however, there was no subsequent sclerification of its cells, 

 the nodal diaphragms of this group being entirely parenchymatous (Williamson, Phil, 

 trans, roy. soc, 1871, p. 505). A similar sclerified periderm has been found by the 

 writer in E. limosum. In E. silvaticum, E. arvense, and E. variegatum, on the other 

 hand no nodal periderm is present. The presence or absence of this feature may be of 

 some use in the difficult task of tracing the relationships of the modern Equiseta. The 

 palaeobotanical writers above referred to compare the periderm of calamitean diaphragms 



