380 REPRODUCTIVE ORGANS OF FUNGI.—HYPODERMIA, 
each of which, like those from the conidia, may settle down and 
produce a new Cystopus mycelium. 
(ii) Hypodermix.—Puccinia graminis, which we will take as 
the type of this group, is remarkable not only in showing a dis- 
tinct alternation of generations, but also in the fact that each 
generation is developed upon a different host, and thus affording 
a good example of what has been called hetereecism, or changing 
from host to host during different changes of development. 
Thus in the spring, the fungus (jig. 836) may be seen in one 
phase of its existence growing on the Barberry (Berberis vulgaris), 
whilst in the summer, upon certain Grasses fungous growths 
(figs. 837 and 838) may be seen which have been developed from 
spores formed whilst the Puccinia was inhabiting the Barberry, 
and which in fact constitute the second generation. 
If a section be made 
Fic. 836. through one of the yellowish 
swellings seen on the leaf of 
a Barberry plant which is 
affected by the fungus, the 
whole tissue of the leaf at 
the spot in question will be 
found to be permeated by 
the mycelium of the Pue- 
cinia, whilst two kinds of 
fructification may be noticed, 
one on either side of the 
leaf. On the upper surface 
(fig. 836, 0) are somewhat 
rounded spaces, termed 
spermogonia, sp, full of very 
delicate hair-like bodies, 
and from the floor of the 
cavity very small spore-like 
structures, the . spermatia, 
Fig. 836. Section through leaf of the Bar- are formed. On the under 
berry infested with Puccinia graminis, o. Surface are the much larger 
Epidermis of upper surface of leaf. sp. seidium fruits or &xcidia, 
Spermogonia. p, p. Layers of cells (peri- 7 
dium), surrounding, a, a, the xcidium %, 4. These consist of 
fruits. After Sachs. closely packed vertical 
hyphee, from which, by a 
process of continuous budding, a great number of conidia-like 
spores are detached. It is by the germination of these spores 
and their growth on Grasses, that what are known as the wredo- 
frwits are produced. 
These uredo-fruits consist of a dense mycelium (fig. 837, sh), 
interwoven among the cells of the Grass leaf, from which 
vertical branches shoot upwards bearing at their extremities 
oval granular spores, the wredospores, wr. These uredospores, 
germinating in other Grasses, again produce wredo-fruits, and 
