306 MR. A. S. HORNE ON THE STRUCTURE AND 
Position in Diagram. Number of Fibres. Remarks. 
BOP ae US e 
89 > Beginning of cork formation. 
10 Trace of endodermis. 
BEAU @ 
D 
© 
0 Complete endodermis. 
The vascular structure of the seedling of Davidia is in a state of flux, and it will be 
shown that this condition prevails not only in the vascular structure of the seedling, 
but also in the building of the inflorescence and the flower. 
The tissues of Davidia—the outer cortex, medullary rays, phloem parenchyma, xylem, 
sheath and nest-cells of the central cortex—are full of starch. Tannin occurs in the 
peduncle and fruit. Calcium oxalate is very generally distributed, more often in crystal 
clusters or in clinorhombic form. The medullary rays are narrow, some two or three 
cells broad. In radial sections the cells are brick-shaped. In some rows the cells 
have their long axis horizontal, in others the cells have their long axis vertical—the 
procumbent and upright cells of De Bary *. Certain cells are septate with single crystals 
in each chamber. The sieve-tubes are of medium size and resemble those described 
by A. W. Hill t for certain Angiosperms. In all the material examined the callus 
areas and markings were prominent, and showed up well when treated with methyl 
blue (Grübler). The companion cells are comparatively large. They are divided by 
thin septa into a number of compartments. Each chamber contains a more or less 
corroded clinorhombie crystal of calcium oxalate. These crystal rows are a charac- 
teristic feature of the phloem. The phloem parenchyma of Davidia consists of rectan- 
gular albuminous cells and squarish or irregularly-shaped crystal sacs, crystal cells, or 
septate crystal cells. Typical hard bast is present in the primary phloem. ‘The fibres 
occur in scattered groups: we do not find in our material the “ gemischten, continuir- 
lichen Sklerenchymring” that Sertorius t describes for Davidia. Fibres occur in all 
parts of the stem and peduncle. As growth proceeds, the fibres, which were originally 
straight, are seen to be arc-shaped in tangential section, due to tangential pulls as in 
Tilia. The walls of fibres of the first-year hypocotyl of Davidia, when treated with 
sulphuric acid and iodine, show three regions—an inner sky-blue band which merges 
into a middle bluish-green band, and a golden brown, less-swelling, limiting layer. 
Fibres of a hypocotyl some years older differ chiefly in the increased thickness of the 
wall, the middle band being the most extensive. There is little increase in the degree 
of lignifieation with increasing age. The fibres of Davidia are intermediate in compo- 
sition between the white ones of Cornus, which contain a large proportion of cellulose, 
* De Bary, Comp. Anat. p. 486. 
+ A. W. Hill in Ann. Bot. xvii. (1903) p. 265. 
$ Sertorius in Bull. Herb. Boiss. i. (1893) p. 623. 
