Primulaceae. 211 



root-hairs. All the wall thickenings in the cortex consist 

 of pure cellulose. It is possible, that the unthickened 

 elements mentioned in the exo- and endodermis, have served 

 as passage-cells for water at an earlier stage of the devel- 

 opment of the roots, before the cutinization of the middle 

 lamella reduced their permeability. The fact that the 

 epidermis keeps alive and active as a water absorbing 

 organ for a long time (I have found well preserved 

 root-hairs nearly up to the base of the root), seems to me, 

 at least, to confirm this supposition. 



Fig. 24, A depicts a transverse section of a root-branch, 

 about 0.5 mm thick; it is two-rayed and both endo- and 

 exodermis are well developed. 



The vascular bundles of the rhizome are arranged 

 in a ring. The number varies somewhat according to the 

 thickness of the rhizome, and I have counted up to 7 in 

 a transverse section. In shape they vary from round to 

 much elongated tangentially ; anastomosis is frequent. They 

 are collateral, and each is surrounded by a strand-sheath, 

 with its cells often divided by thin radial walls. Outside 

 the vascular-bundles, a "réseau radicifère" is formed (see 

 Decrock p. 183 and 196), from, which the adventitious 

 roots initiate. The ground-tissue consists of fairly thick- 

 walled, many-pitted cells, containing some starch (July). 

 There was an active cork -cambium directly under the 

 epidermis, on the part of the rhizome formed the pre- 

 vious year ; the cells of the cork contained a brown 

 substance. 



The peduncle. The stereome, so common in the 

 Primulaceae, is very slightly developed here; it encloses a 

 circle of 15 — 20 vascular bundles, and to some extent, it 

 surrounds each single strand. A quickly perishing ground 

 tissue is present in the middle. Outside the stereome, an 

 assimilative parenchyma with large intercellular spaces is 



14* 



