Feb. 16, 1924 
Flag Smut 0} Wheat 
479 
Although the possibility of ‘‘ Triebinfektion ’’ is admitted, it is felt 
that such a source of infection of secondary shoots probably is of less 
frequent occurrence than infection of such shoots by mycelium already 
present in the plant. 
DEVELOPMENT OF THE ORGANISM AND ITS RELATION TO THE HOST 
INTRODUCTION 
A study of the germination of the spores of Urocystis tritici has indi¬ 
cated that there may be considerable variation in the morphological 
character of the promycelium and of the sporidia. It is an interesting 
fact that sporidia are formed not only in air but also within a liquid 
substrate. This rather suggests that the physiological constitution of 
these bodies is different from those produced by most members of the 
Tilletiaceae, for it usually is considered that the members of this family 
produce sporidia only in air. 
Brefeld (3, p. 175, 212, pi. 11) has discussed the morphological fea¬ 
tures of the germination of Urocystis ranunculi , U. occulta (Wallr.) Rab., 
and I/, filipendulae Tul. Sporidial structures are produced by these 
species, but he has questioned whether they should be considered 
as sporidia and has suggested that perhaps they are sterigmata, which 
no longer produce sporidia. McAlpine (29), on the other hand, states 
that the structures produced by the promycelium of U. occulta should 
be considered true sporidia because they germinated by putting forth a 
germ tube. More recently Paravicini (36) has stated views similar to 
those advanced by Brefeld. 
The spores of Urocystis tritici resemble those of U. occulta in many 
respects. The character of the germination of the spores also is 
practically the same in each species. Hence, it was thought that a more 
detailed study of the germinating spores of U . tritici , especially 
with reference to the nuclear phenomena involved, might yield more 
exact information on the nature of the structures produced and their 
significance in the propagation of the organism. 
A number of investigators have studied the nuclear phenomena 
involved in various phases of the life history of many smuts. In this 
connection attention was first directed to the nuclear condition in the 
young spore. Dangeard (10) studied the development of spores in a 
number of* genera of the Ustilaginaceae and Tilletiaceae and found that 
the young spores consistently contained two nuclei which later fused. 
This fact has since been confirmed by Maire (33), Lutman {28), Rawit- 
scher (41), and others. 
In a discussion of some features of the germination of spores of certain 
of the Tilletiaceae, Dangeard (10) also stated that the nonseptate pro¬ 
mycelium of Urocystis violae (Sow.) F. de W. and Tilletia caries Tul. 
contained eight nuclei derived from the single fusion nucleus, and a 
single nucleus then passed into each of the eight sporidia. 
A similar observation has been made by Paravicini (36) for Tilletia 
tritici (Bjerk.) Wint., Entyloma calendulae (Oud.) de B., Urocystis anem¬ 
ones (Pers.) Wint., and U. violae (Sow.) F. de W. In these forms he 
states that typically a nucleus wanders to the end of the promycelium 
and divides there several times, a single nucleus then passing to each of 
the sporidia. 
