33^^ 



PRIMARY ARRANGEMENT OF TISSUES. 



palustre (145). « Endodermis. / axial air-canal, at x 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 wide intercellular passage, 

 in which the letters r, t, s are written. / 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. 1 50 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 



ric. 150. 



the stem, g-g, s, r, 1, the xylem, -n 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 

 inner 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, g and g a transverse group of narrow pitted vessels. A sheath composed 

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

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



