1912] GRIGGS—RHODOCH YTRIUM 171 
32. VUILLEMIN, Paut, Les bases actuelles de la systematique en Mycologie. 
Prog. Rei Bot. 2:40-170. 1907. 
33. WILLE, N., Nachtrage zu map eae in ENGLER and PRANTL’s Pflan- 
seniceuition, Nachtr. zu 17:48-49. 1900. 
_ EXPLANATION OF PLATES XI-XVI 
he figures were made with various combinations of Zeiss apochromatic and 
Spencer achromatic oil immersion lenses with compensating oculars. 
magnification of the different figures is given in the description of each. The 
figures have been reduced one-third in reproduction, canceling the enlargement 
due to the camera and rendering them the same size as when seen in the 
microscope. . All of the figures, except 16 and 19, were taken from the race of 
the parasite on Ambrosia artemisiifolia. 
Fic. 1.—Young resting spores; XX 33 
Fic. 2,—Somewhat older resting ae spreading out irregularly in the 
tissue; X 334. 
Fic. 3.—Cyst in which the basal portion has swollen out, although the 
protoplast has grown but little; rhizoids not in plane of section; nucleus with 
numerous spherules of chromatin connected by linin strands scattered through 
its cavity; X334. 
Fic. 4.—A full-sized resting spore whose wall is beginning to thicken, with 
that portion of the rhizoidal system which lay in the plane of section; x 334. 
IG. 5.—A portion of .the rhizoidal system of a mature cyst, showing its 
relation to phloem and xylem; X 334. 
Fic. 6.—Detail of a haustorium closely applied to a pitted vessel; from a 
cyst which had surrounded itself with a thick wall, hence the wall around the 
haustorium; X 334. 
Fic. 7 A Desay es resting spore, showing the shriveling of the nucleus 
and the cutting off of the rhizoids; X 334. 
Fic. 8—Mature three-layered resting spore; 334 
Fic. 9.—Starch grains from mature cysts, showing variations in size and 
shape; X 2000. 
Fic. 1o.—Starch grains from a mature cyst under polarized light; X 2000. 
IG. 11.—Young zoosporangium with numerous fine strands of cytoplasm 
in which starch is forming; 334. 
IG. 11a.—Detail from fig. 11, = formation of starch grains; X 3000. 
Fic. 12,—Young zoosporangium 334 
rig . Te zoosporangium yi tagivning to swell out; 
ng zoosporangium in the stem of the host; plug Guaty 
drt aithousl the tubular form is still retained; X 334. 
Fic. 15.—Full-sized zoosporangium, showing the characters of the primary 
cyst; x 334. 
Fic. 16.—A typical turbinate plug from the race on Asclepias pumila; 
X 670. 
