36 MacDougaL — Symbiotic Saprophytism . 
The roots of Pterospora branch exogenously. The seven 
to ten layers of the cortex are composed of ovoid cylindrical 
elements with the tangential greater than the radial diameter, 
an important deviation from the general arrangement of this 
tissue in the roots of saprophytes. The subepidermal layer 
undergoes radial division in older cells during or after 
exfoliation of the epidermis. Storage-material in the form of 
starch is to be seen in the cortex of the apical portions. The 
central cylinder resembles that of Monotropa most closely. 
The tracheal elements are lattice-cells. Secondary thickening 
occurs, while sclerotization and lignification are entirely 
lacking in contrast with Sarcodes. The periblem and plerome 
are easily separable. The entire embryonic region is heavily 
loaded with starch, staining first a reddish brown then 
a bluish black with iodine solution. 
The Shoot. The shoot of Pterospora consists of a short 
rhizome which sends up each year a cylindrical stem bearing 
a terminal raceme of pendulous flowers and a number of 
scale-leaves of reduced size. The stem-system of this plant 
exceeds that of the root many times in bulk, and it exhibits 
minor anatomical differences from Monotropa and Sarcodes , 
chiefly as a physiological result of its immense size. The 
medulla is from 3 to 6 mm. in diameter, making up about 
half of the cross-section of the stem, and is composed of 
cylindrical elements with ample intercellular spaces. The 
fibrovascular bundles contain one or two annular and two or 
three spiral vessels, with a few elongated elements of slight 
differentiation which are perhaps tracheides. A number of 
closed sieve-tubes are present. The xylem-bundles do not 
form a ring, but immediately external to the bast-region is 
a complete cylinder of heavy sclerenchyma composed of 
ten to fifteen layers of cells. Both the xylem and the 
sclerenchyma are distinctly lignified. Of other saprophytes 
examined, a species of Bur Manilla alone exhibits lignifica- 
tion of the shoot (Groom, 13). The cortex is composed of 
cylindrical elements arranged in circles with intercellular 
spaces which increase in size outwardly. The two or three 
