312 
Groom . — A Note on the Vegetative 
sylvestris , especially as their lumina are narrow. But the inmost tracheides, 
often exactly one series, of the annual ring show wider cavities than else- 
where, and thus represent a microscopically thin £ pore-zone 1 of spring- 
wood. 
The bordered pits of the tracheides are mainly on the radial walls, 
where they are by no means abundant, being uniseriate even in the 
spring- wood ; their fusiform apertures are spirally directed, and in the 
summer-wood exceed in length the diameter of the chamber. Bordered 
pits also occur on the tangential walls, more especially of tracheides 
forming the outer boundary of the annual ring. 
The medullary rays are all uniseriate and remarkable for their shallow- 
ness, being usually only i to 4, occasionally 5, cells in height. They consist 
solely of thin-walled parenchyma, in the lateral radial walls of which the 
pits are nearly equal to the height of the cell, or each pit of such a kind is 
replaced by two superposed ones. 
The Leaf. 
The leaf is xerophytic in structure. In the first place the epidermis has 
a thick cuticle and otherwise thick walls, while the stomata are sunken. 
Secondly, there is a single layer of thick-walled hypoderma, which is 
continuous except within the stomatic apertures. 
Contrasting with this tegumentary system is the very loose green 
tissue lying within and simulating palisade-parenchyma though excavated 
by a large intercellular system. 
The centre of the leaf is occupied by a strand that is denser in structure, 
except that it includes a large median ventral resin-duct. The feature 
worthy of special note is the extensive development of the transfusion-tissue 
in comparison with the puny xylem proper. 
The stomata are restricted to the upper face of the leaf, where they are 
ranged in several longitudinal rows. In each row the successive stomata arc 
mostly separated merely by a single short epidermal cell, but nearer the 
ends of such a row these single short cells become replaced by longer ones, 
or by only two or several cells. The longitudinal rows of stomata are 
separated laterally from one another by only two lines of epidermal cells. 
The communication of the stoma with the internal atmosphere of the 
leaf is sharply limited. For within each stoma the gap not only in the 
thick-walled hypoderma, but also in the mesophyll lying within, is very 
small ; indeed the interruption in the latter tissue is limited to the local 
separation of either two or three cells, which, in surface section, bound 
an intercellular space whose oval outline approximately coincides with the 
periphery of the guard-cells. 
The hypoderma at certain isolated spots, in transverse section, is 
as much as three cells in thickness. 
