MILDEWS, RUSTS AND SMUTS 
63 
ciliated that the annual loss to cultivated plants throughout 
the world, caused by fungi alone, amounts at least to 
£250,000,000 sterling. The loss due to animal, mostly 
insect depradations, exceeds this amount. 
According to the Prussian Statistics Bureau, the loss from 
rust of cereals alone amounted to £20,000,000 during one 
year. In the United States £3,000,000 represents the loss 
due to rust of wheat in one season. In Australia a dead 
loss of £2,500,000 was occasioned by the rust of wheat 
in a single season. 
Heteroecism 
This term implies that during different periods in the 
life-cycle of a fungus, it is parasitic upon two different 
host-plants. This remarkable phenomenon although not 
confined to members of the Uredinaceae, is most prevalent 
there and reaches its maximum in the genus Puccinia, 
although it is not confined to this genus. When a fungus, 
as in the great majority of instances, completes its entire 
development on one and the same host-plant, or matrix, 
it is termed autoecious. On the other hand, where a fungus 
lives during different periods of its development on two 
distinct host-plants, it is said to be heteroecious. As ex¬ 
amples of heteroecious species, Puccinia sylvafica has its 
aecidial stage on the living leaves of the dandelion, and its 
uredo- and teleutospore stages on the living leaves of vari¬ 
ous sedges. The aecidiospores produced on the dandelion 
cannot directly infect another dandelion plant, but can 
infect the leaf of a sedge, and commence the uredo condition 
of the fungus. The uredospores produced on the sedge, 
can on the other hand, infect other sedges, and this continues 
so long as sedges are in active growth, but when the vitality 
of the sedge begins to wane, the mycelium that has been 
producing uredospores, now produces teleutospores. The 
teleutospores, unlike uredospores, cannot directly infect 
sedges, but after a period of rest, germinate the following 
season, and infect dandelion leaves, thus completing the 
cycle of development, and commencing a new cycle. 
Puccinia graminis, or wheat rust, when it passes through 
all the phases of its development, commences by producing 
its aecidial stage on living leaves of the barberry. The 
aecidiospores cannot infect other barberry leaves, but can 
infect the leaves of the wheat plant. This infection gives 
origin to the uredo stage, and the uredospores produced 
continue to infect other wheat plants throughout the grow- 
season, thus, as previously explained in connexion with the 
