436 BOTANICAL GAZETTE | DECEMBER 
and shape, the outer walls being strongly cuticularized (fig. 2, 
ep); (2) thin-walled stereomatic cells (jig. 2, st); and (3) 
thick-walled stereomatic cells (fig. 2, st). Both the thin-walled 
and the thick-walled stereomatic cells give the characteristic 
reaction for lignin with thallin sulfate, phloroglucin, and anilin 
sulfate.® 
Neither the thick-walled nor the thin-walled stereomatic cells 
occur with any great degree of regularity in the cortical region. 
Frequently only the thin-walled cells are present, and then again 
there may be a definite layer of thin-walled cells next to the 
epidermis proper, with scattering thick-walled cells beneath. 
The more common arrangement is that in which both thick- 
walled and thin-walled cells are indiscriminately mixed, the 
whole forming a ring of tissue, which gives strength and rigidity 
to the needles. 
At various points the stereomatic tissue is interrupted by the 
stomata (fig. 2). These occur on both sides of the leaf and are 
generally considerably depressed, as is the case with the other 
pines and plants having thick epidermal parts. The stomatic 
furrows are filled with a waxy substance, which probably plays 
an important part in preventing the entrance of fungi, and also, 
as Wilhelm? has pointed out, serves as a check to transpira- 
tion. | 
The mesophyll region occupies the median portion of the 
leaf, occurring in a zone which varies in thickness from 200 to 
300 w. The cells composing it are large and thin-walled, and 
contain, among other things, chlorophyll, starch, and the usual 
contents of assimilative tissue. In cross-sections the cells are 
seen to be nearly polygonal in shape and joined more of ai 
closely in rows arranged at right angles to the cortical region. 
The number of rows vary according to the conditions srt 
which the leaf is grown, those in intense light having, as Stahl ; 
°BEHRENS: Tabellen zum Gebrauch bei mikroskopischen Arbeiten, 1892. 
7 Ueber eine Eigenthiimlichkeit der Spaltéffnungen bei Coniferen, Ber. d. dew 
Bot. Ges. r: 325. 1883. ; 
® Ueber den Einfluss der Lichtintensitat auf Structur und Anordnung des Assim- 
ilationsparenchyms, Bot. Zeit. 38: 868. 1880. 
tsch. 
