1897] NORMAL AND DISEASED ORGANS OF ABIES BALSAMEA 317 
side of the leaf. At the base and apex of the leaf the bundle is 
undivided; but in the middle, and for the greater part of its 
length, it is bifurcated. The phloem part (dorsal) consists of 
smaller and less thickened cells than those of the xylem (ven- 
tral). The phloem and xylem cells are arranged in more or 
less distinct rows, usually separated by medullary rays. The cells 
of the medullary rays frequently contain crystals of calcium 
oxalate. 
2. Diseased leaves —The diseased leaves are about one-half 
to three-fourths as long as the normal ones on the lateral 
branches, but they have about the same length and thickness as 
the leaves of the terminal shoots. The diseased leaves growing, 
as they do, on negatively geotropic branches, are more or less 
homologous to the normal leaves of the terminal shoots. In 
comparing the anatomy of the diseased and the healthy leaves, 
those of the lateral shoots should be considered. In Hart- 
mann’s comparative anatomical study of the witch broom of A. 
pectinata the leaves of the lateral branches only are considered. 
The cuticle of the diseased leaves is less thickened than that of 
the normal leaves. The number of stomata and stomatal rows 
varies according to the size of the leaf, as well as to the severity 
of the mycelial infection. There are only about one-half as 
many stomata in the diseased as in the normal leaves. 
The epidermal cells vary greatly in size; they have larger 
lumina than the normal and are less thickened, especially on 
their inner sides, which are seldom laminated, or provided with 
_Pore canals. The hypodermal cells are present, especially in 
the basal half of the leaf. They are more irregularly distributed, 
often forming nests and groups. The cells are often twice as 
large and thick walled as the normal hypodermal cells (fg. 4). 
As in the normal leaves, the number of hypodermal cells 
decreases from the base toward the apex, but with the decrease in 
: the number of hypodermal cells an increase takes place in the 
oe mber of stomata on the upper and lower leaf surfaces. On 
* | SScount of the unequal thickening and irregular distribution of 
mal and hypodermal cells, the diseased leaves shrivel 
