33° 



PRIMARY ARRANGEMENT OF TISSUES. 



palustre (145). a Endodermis. i axial air-canal, at *• remains of the membranes of 

 shrivelled pith-cells. In the middle a vascular bundle surrounded by parenchyma, with- 

 out a distinct sheath. At the inner edge of the bundle lies a vi^ide intercellular passage, 

 in which the letters r, t, s are written, t an annular fragment, adhering to the wall, of 

 the membrane of a primitive tracheide for the most part destroyed, r persistent 

 annular tracheides. g groups of the last developed, likewise permanent, annular and 

 reticulated tracheides, distinguished from the surrounding tissue by the shading of 

 their walls, s the phloem ; in this the wider lumina belong to the sieve-tubes (cp. p. 

 180), the narrower ones, some of which are granularly dotted, to the cambiform -cells. 

 The double-contoured bands on the outer edge of the phloem, inside the layer of cells 

 following a, indicate the collapsed primitive elements of the phloem (Protophloem). 



Figs. 150 and 151 represent two cross-sections through a bundle of the leaf-trace of Zea 

 Mais, at different parts of its course. Fig. 150 (550), from Sachs's Text-book, is from 



FIG. 150. 



the stem. g-g,s, r, I, the xylem, -v the phloem. In the latter -v, -v indicate the sieve- 

 tubes, between which the -narrower cambiform cells stand in regular distribution. At 

 the outer edge of the phloem are its narrower, thick-walled primitive elements. On the 

 fnner edge of the xylem in an intercellular passage, /, bounded on the outside by the ring, 

 r, of a primitive annular vessel, partly destroyed by the longitudinal extension, s spiral 

 vessel, g, g large vessels with (unbordered) pits, or narrowly reticulated. Between the 

 phloem and s, ^ and ^ a transverse group of narrow pitted vessels. A sheath composed 

 of sclerotic lignified elements goes all round the bundle ; f, f thin-walled parenchyma 

 outside the sheath, a outer edge, i inner edge of the whole bundle. In the lamina of 



