140 Gibson. — Contributions towards a Knowledge 
the phloem contains true sieve-tubes. The bundles are 
cauline at first, and derived from elongated procambial cells ; 
leaf-traces are inserted later on the margins of the bundle. 
Although I am not at present prepared to speak on the 
development of the tissues in Selaginella , still I may say that 
no tracheides appear above the point of insertion of the 
youngest leaf-trace. The cell-layer which gives rise to the 
lacunar tissue, Treub describes as dividing tangentially into 
i°, a layer next the vascular system, the cells of which develope 
local annular cuticularizations on their walls, and 2°, an outer 
layer whose elements divide radially. 
The accounts given by Sachs and De Bary may next be 
referred to. Sachs (15) draws attention to the absence of 
intercellular spaces in the cortex (a statement which, as will 
be shown hereafter, is by no means of general application) 
and to the cauline nature of the vascular bundles on which the 
leaf-traces are afterwards inserted. His account of the anatomy 
of the stem is fundamentally that given by Russow. 
Further details are given by De Bary (16). He follows 
Russow in describing the vascular bundle as of the fern-type, 
and like that author considers a true endodermis to be absent. 
Probably the majority of the species have, De Bary says, one 
axile ribbon-shaped bundle, some having on the middle of the 
upper surface a median ridge. The leaf-traces are inserted on 
the margins of the axile strand. 5. Kraussiana , 5. Galeottei , 
and others are noted as having two axillary bundles. (This, 
however, is true only of the region between the points of origin 
of branches, and in some species even there the steles are 
connected by pericyclar tissue). Reference is also made to 
S. inaequalifolia with three vascular bundles (there are fre- 
quently as many as five, and these gradually fuse into one in 
the creeping portion of the stem) and to .S'. Lyallii with e ten 
or twelve bundles distributed in three equidistant rows in an 
almost quadrate surface ’ (this is true only of the upper parts 
of the erect shoots), and to S. spinosa , where the single axile 
bundle has leaf-traces inserted on it all round. (Here again 
the creeping portion of the axis has an entirely distinct 
