ae ee Lame, 
LEITNERIA FLORIDANA. FT 
tudinal section they often appear as rectangles, with their 
greatest diameter transverse. Their walls, which are very 
thin, show, nevertheless, a decided secondary thickening, 
and are marked by simple pits, as is usual in pith of this 
description. Toward the wood, and especially where the 
pith rays pass outward to the branches, occasional cells in 
more or less marked vertical rows occur, with large stellate 
crystals. 
At the margin of the pith a number of layers of cells of 
reduced diameter but several times as long as the pith cells, 
constitute a pith sheath, and gradually merge into what 
are virtually wood parenchyma cells. They have the same 
simple pits as the pith cells, but are arranged in vertical 
rows in relation with the elements of the xylem, and vary 
in length from twice to four or five times their diameter. 
In the mass of parenchyma so formed at the margin of the 
pith, are found intercellular secretion reservoirs, each of 
which is surrounded by a layer of oblong secreting cells 
with walls not appreciably thinner than those of the paren- 
chyma immediately about them. From one to two dozen 
such passages are to be seen in a cross section of the stem.* 
Though as a rule they occur singly, it is not uncommon for 
two of equal size to stand close together, separated by only 
a few layers of cells, or for small ones to stand on one or 
both sides of a larger one. The secreting cells are usually 
* These were formerly attributed by Van Tieghem (Ann. des Sci. Nat. 
7 ser, i. 64, and Van Tieghem and Lecomte, Bull. Soc. Bot. de France, 
1886, xxxiii. 182) to the apexes of the primary xylem wedges, but, ac- 
cepting as the inner limit of the wood, the position of the innermost 
vessels, Professor Van Tieghem now recognizes these secretion pas- 
sages as pertaining to the pith (Morot’s Journal de Botanique, v. 384, 
385), thus coming into agreement with Miiller (Engler’s Bot. Jahr- 
biicher, ii. 449), Burck (Amn. Jard. Bot. Buitenzorg, vi. 151), and Heim 
(Ass. Frang. p. l’Avanc. des Sciences, 1891, i. 231; Rech. s. les Diptéro- 
carpacées, Thesis, 1892, 175), who have attributed the similarly situated 
passages of Dipterocarpeae to the pith. But Reinsch, Engler’s Jahrb. xi. 
374, speaking of the Balsamifluae, again calls attention to their close con- 
nection with the xylem, and, indeed, it appears extremely difficult so to 
define the hadrom bundle as unequivocally \to separate it from the 
adjacent pith. 
13 
