: Special MM. orpholosy and Classification. 281 
least during the early period of growth, only of a single tubular cell. 
They therefore present a point of transition to the Algze through the 
Vaucheriee. The Safrolegniee (Figs. 401, 402) usually grow on the 
bodies of insects putrefying in water, and cover them completely with 
radiating tufts. An alternation of generations takes place in them 
between individuals which produce swarmspores and oospheres. The 
Peronosporee live within the tissue of Phanerogams, the branches of the 
mycelium penetrating between the cells, and drawing their nutriment 
from them by means of special organs, the austoria. The mycelium 
produces first receptacles from which conidia are abstricted, and these 
always project above the surface of the host,—in /%ronospora through 
the stomata. These conidia are not usually immediately capable of germi- 
nation, but only in contact with water, as drops of dew and rain, develope 
a few swarmspores (Fig. 400), which attach themselves to the surface of 
a plant, and put out germinating filaments which penetrate into it ; 
and the cycle of development then begins afresh. Under favourable 
circumstances oogonia ancl antheridia are produced at the extremities 
of the mycelial threads, but only in the interior of the plant. The 
oospores either form swarmspores or germinate directly. eronospora 
zufestans is the cause of the potato-disease. The Jucorimt are pro- 
pagated by conidia and spores formed in sporangia (ascospores) as well 
as by zygospores. Their root-like branches afterwards become multi- 
cellular by the formation of septa. The common green and brown 
moulds, AZucor AMucedo and Penicillium glaucum or crustaceum belong 
to this family (Figs. I, p. 7, and 396, p. 267). Luxuriant conidio- 
phores of these Fungi sometimes unite into a leaf-like arborescence, 
known as Coremium. The term ‘mould’ is not one of scientific 
exactness ; in popular language the name is applied to flocculent and 
filamentous structures which form on decomposing organic bodies. 
Il. HYPODERMI/. 
a, Uvredinee. . Ustilaginee. 
These Fungi live in cellular tissue, usually beneath the epidermis 
of flowering plants. They all ferm resting-spores, from which, under 
favourable circumstances, ecidia and spermogonia are developed in 
the Uredinee, but not in the Ustilaginee. To this class belong Ustclago 
carbo, the ‘smut’ of cereal crops, and Puccinia graminis or ‘mildew’ 
(Figs. 406, 407, pp. 272 3). 
