99 



closely to the ' similar structure („Ringholz") of Vhytocrene. 

 The elements which compose this wood are of two kinds as 

 may be seen even in cross-section , namely tracheal and cellu- 

 lar. Their diameter is however uniformly small and their walls 

 about equally thickened, which together with the fact that 

 the elements are closely applied to one another, leaving scar- 

 cely perceptible intercellular spaces, gives this ring of first 

 formed secondary wood a considerable degree of firmness , rea- 

 dily noticeable in comparison with the rather loosely built 

 xylem later formed. In fact the latter can without great dif- 

 ficulty be entirely stripped off a stem of the size in question 

 without injuring the inner zone. If now the elements of this 

 early formed secondary wood of lodes be investigated further 

 by means of macerations and longitudinal sections, it will be 

 seen that they are not histologically identical with the simi- 

 larly arranged elements in Phytocrene. The tracheal elements 

 in Phytocrene although very long and narrow, still stand in 

 communication with one another near their ends by elliptical 

 apertures, and thus form vessels; in lodes on the other hand 

 only those tracheal elements which continue the rows of the 

 primary bundles and perhaps not all of them, have the cha- 

 racter of vessels , while the intermediate rows of treacheal ele- 

 ments are typical tracheids. The cellular elements of this ring 

 of wood in Phytocrene , it will be remembered, have the pecu- 

 liar form of blunt, septate fibre-cells. In lodes however the 

 wood-cells , which occur in rows between those of the tracheids 

 and vessels, are not only very much shorter but lack the 

 division by unthickened, cellulose cross-walls. These cells arise 

 like those of many medullary rays, singly from short cam- 

 bium-cells without subsequent transverse division, their walls 

 sufiTering a considerable lignification. The xylem-ring just de- 

 scribed is elliptical, its maximum diameter coinciding with the 

 shortest diameter of the stem, it thus extends nearly from 

 side to side of the stem-cross- section , as may be seen in Fig. 1. 

 After this ring of wood which attains an average breadth 

 of 8 — 15 cells, being a little thicker at the ends of the ellipse 



