149 
9. The large black linear sori extending up and down the stem,— 
the telia. Most of them have ruptured the epidermis, exposing the black 
spore-mass within. 
10. The thin epidermal covering, ruptured in most of the telia 
but partially or wholly covering others. 
ll. The telia developed on the inflorescence. What organs 
are affected? ‘ 
12. Kernels from badly diseased plants in comparison with 
those from healthy plants. How do they appear to be affected? Telial 
sori are occasionally developed under the seed-coat of the kernel. (See 
Phytopath. 1:150-154, fig. 1-2.) 
SKETCH an internode and also parts of the inflorescence to show the 
black rust symptoms. Make an enlarged DRAWING of a telium as seen 
under the hand-lens. 
ETIOLOGY 
The black rust of cereals and grasses is caused by the fungus, Puccinia 
gramints Persoon. It is one of the Uredinales which are perhaps the most 
highly specialized of basidiomycetous pathogenes. It is a heteroecious 
parasite producing its aecial structures on the barberry, a host widely 
remote in relationship from its grass-hosts on which the other spore- 
forms appear. This species, Puccinia graminis, includes a variety of 
biologic forms, morphologically alike; and all having their aecia on the 
barberry but restricted rather sharply in their uredinial and telial stages 
to ca cereal- or grass-hosts. (See McAlpine, Rusts of Australia, 
p. 122. 
Life-history. This pathogene produces, during its life-history, all the 
known fruiting structures of the rust-fungi: pycnia (O), aecia (I), uredinia 
(II), telia (III), and basidia (IV), each with their characteristic spores. 
It is therefore said to be a Eupuccinia, that is, a true Puccinia. (See 
McAlpine, Rusts of Australia, p. 10-11.) 
The Primary Cycles are normally those which develop only upon the 
barberry and exhibit the pycnia and aecia. It seems certain, however, 
that the fungus may winter over in the uredinial form (probably as my- 
celium) and by uredospores initiate primary infections on grass- and 
cereal-hosts. This second type of primary cycle is essentially secondary 
in all respects except as to the time it originates. It will not be considered 
separately in this exercise. 
Pathogenesis. The inoculum for the primary infections consists 
of the basidiospores (sporidia), produced on the basidium (promycelium) 
from the overwintered teliospores on diseased straw. Examine the 
germinated teliospores on slides or study the drawings provided, and 
OBSERVE :-— 
13. The long slender basidium put forth from each cell of the 
teliospore; 4-celled near the apex. 
14. The long pointed sterigma from each basidial cell bearing at 
its apex a thin-walled ovoidal basidiospore (sporidium). Each sporidium 
contains one nucleus and finely granular protoplasm. _ 
DRAW or copy to show sporidia ready for dissemination. 
These sporidia are carried by the wind or splashing rain to nearby bar- 
berry bushes where, in the moisture on the surface, they send forth a germ- 
tube which penetrates the tender epidermis and gives rise to the locally 
