Scrophulariaceae. 417 



walls. In the endodermis — contrary to Hovelaque, who 

 mentions its cells as being "sans cadres" — I found distinct, 

 although rather faint, Casparian dots, The outermost layers 

 of the stele consist here of rather thin-walled hgnified prosen- 

 chymatous cells; the sieve-tissue forms a continuous ring 

 outside the xylem-part, which in the whole extent of its 

 periphery consists almost exclusively of wood-fibres. The 

 pith consists of thin-walled cells which collapse early in the 

 centre of the stem. 



A section taken at about the middle of the subterranean 

 part of the axis, is distinguished from the above by having 

 a more distinct endodermis, the cells of which have, as in 

 the root, a suberised lamella in the whole circumference of 

 the wall — the contents of the endodermal cells have a 

 brown colour — , by entirely wanting hard bast, or at any 

 rate, by having it only in a far more slightly developed 

 degree (in the two diagrammatic figures, Fig. 17, ^ and B, 

 the line between the outer edge of the xylem-ring and the 

 periphery is the endodermis, the black dots ^^'ithin this, in 

 Fig. B, are small groups of hard-bast cells — in ^ these 

 are totally wanting), and lastly, by a comparatively nar- 

 rower pith and broader xylem-ring, in which wood-fibres 

 are less numerous and thin-walled. 



At the point of transition between rhizome and the 

 aérial stem, the hard-bast appears successively (the cells of 

 the hard-bast are here somewhat more thick-walled than at 

 the top of the shoot), the pith widens, the xylem-ring becomes 

 thinner and richer in wood-fibres throughout its periphery. 

 The sieve-tissue is divided into four larger groups, since the 

 hard bast and the wood-fibres of the xylem-ring at four 

 points which decussate, tend to approach one another, and 

 may practically coalesce at these points (this phenomenon 

 is connected with the passing-out of the leaf-trace-bundles 



