Scrophulariaceae. 383 



without intercellular spaces; the walls show the reaction of 

 cellulose. During the growth in thickness of the stele, the 

 endodermal cells are stretched tangentially, and become sub- 

 divided by 2 — 4 thin radial walls; the walls of the original 

 endodermal cells show Casparian dots, but only faintly. The 

 cortical cells contain starch; root-hairs occur in great num- 

 bers. In the xylem portion I have not found indication 

 of annual rings (the root figured is several years old) as in 

 the foregoing species; consequently, the roots complete their 

 development in the course of one year. The xylem is 

 composed of vessels and wood-fibres. 



The Stem. As in V. saxatilis the xylem, in the first 

 year of growth, when the shoots are but weak, frequently 

 consists only of scattered vessels with intervening non- 

 lignified parenchyma, and not until the second year is a 

 continuous ring of vessels and wood-fibres formed, as shown 

 in Fig. 7, which shows a portion of a transverse section of 

 the basal, persistent part of the shoot. I never found more 

 than 3 years' growth in thickness, not even in shoot-bases 

 apparently older. The vessels are comparatively numerous, 

 and the wood-fibres are more sparingly present and also 

 more thin-walled than in the foregoing species. In the cells 

 of the long-lived epidermis tannin is found; cork-formation 

 does not take place, neither in the stem nor in the root. 

 The cells of the cortex contain chlorophyll-grains. The young 

 shoots are beset with glandular hairs of the same type as 

 those on the leaf. In the upper part of the stem, which dies 

 away after flowering, the wood-ring is of course formed 

 entirely during one growth-period, here it is thinner than 

 in the lower part; the cortical cells are thinner-walled and 

 richer in chlorophyll, and the epidermis contains no tannin. 



The Leaf. The epidermal cells of the upper surface 

 have slightly, those of the lower surface more highly, un- 



25* 



