nmm sP

BIOLOGY 15
less than the normal, in spite of an increased rate of assimilation (KoursanofF,
1926). The dwarfing effect of a smut on a grass is well illustrated by the fact that
plants of Agrostis tenuis infected by Tilletia decipiens are so stunted that they
were described as a distinct species (see p. 86).
U. hypodytes, which attacks several forage grasses, causes sterility, long leafy
shoots developing in place of normal inflorescences. The morphology and
anatomy of such diseased shoots in Elymus arenarius and the distribution of
mycelium have been described by Viennot-Bourgin (1937) and by Bond (1940).
A peculiar type of proliferation, whereby individual flowers are replaced by
leaves, stems, and rudimentary panicles, is often seen in sorghum infected by
head smut, Sphacelotheca reiliana (Potter, 1914). Finger-like galls develop from
the axillary buds of Panicum antidotale attacked by Tilletia tumefaciens Sydow
(Mundkur, 1944), and tuberous bodies up to an inch in length are formed
from underground shoots of Lamium album infected by Melanotaenium lamii
(Plate II, Fig. 1).
FORMATION OF THE CHLAMYDOSPOEES '
The formation of a sorus is preceded by the massing of mycehum in that part
of the plant where spores are destined to develop. The details of sporogenesis
appear to differ with the species. Comparatively few have been examined in
detail, none in recent years. A few types have been selected here for individual
consideration.
USTrLAGiNACBAE. Lutman (1910) described the development of spores in the
oat race of Ustilago hordei as follows: ' The first indication of spore formation
in the fungal hyphae is a much branched and contorted condition of some of the
hyphal tips. These are at the same time inter-cellular and this knotting up of
the hyphal tips frequently occurs at the angles of the host cells where they may
be wedged apart considerably. These swollen ends of the hyphae are multinucleated,
each one containing ten to fifteen nuclei. The cell walls now begin
to gelatinize from the inside, a clear zone appearing between the protoplasm and
the darker staining wall. The nests or pustules of hyphae continue to grow and
swell and their waUs become so completely gelatinized at this stage that all that
seems to be present is a tangle of hyphae of irregular shape and varying diameter,
without walls, and lying in a clear matrix. At the same time, the walls
of the host cells immediately adjacent lose the capacity to take up the stain,
the gelatinization of the fungal walls having apparently extended to the walls
of the host cells also.' The changes in the ceU wall, referred to by Lutman and
by others as gelatinization, appear to accompany sporogenesis in several
members of the Ustilaginaceae. The chemical changes involved have not been
studied. A visible swelling is associated with a loss of staining capacity, with
the result that the protoplasts appear in sections as deeply stained masses
separated by a clear space, the gelatinized wall. The development of spines
within the gelatinous matrix has been studied recently by Hutchins & Lutman
(1938) (see p. 50).
Lutman was unable to distinguish the nuclei with certainty in U. hordei, but
he suggests that the small, somewhat angular segments of hyphae finally
separated are binucleate. They become round, develop a thick waU, and form