Fungi. 203 



but of great beauty and elegance. In some the spores are formed on 

 threads which are united so as to form a compound stem. The Dematicx 

 (black moulds) and the Mucedines (white moulds) belong to this family. 

 The threads or stems of the Dematiei have an investing or cortical layer 

 like bark, which may be peeled off, and both the threads and spores are 

 generally more or less colored a dull, dark color, as if charred or 

 scorched. In many cases the spores are large and elongated, and sub. 

 divided by several cross-partitions or septa, the protoplasm of each 

 apartment containing a nucleus. The Helminthosporium constitutes a 

 numerous genus of the black moulds, and is found in patches like velvet 

 on decaying herbs and old wood. The spores are produced on upright 

 stems or threads shooting up from the matted mycelium, and grow out 

 of the top or sides. The cortex or bark of the stem adds to their stiff- 

 ness. Under the microscope these stems appear jointed like canes in a 

 cane-brake. 



The most important genus of the Mucedines is the Peronospora. The 

 various species of this genus are parasites on living vegetables, and one 

 of them is the cause of the potatato disease, which has played such 

 havoc with the Irish potato. In this genus there is a delicate mycelium 

 which penetrates the intercellular passages of living plants, giving rise 

 to erect branch threads which bear, at the tips of their outermost twigs, 

 oval or spherical-shaped spores called conidia. There is no cortex on 

 them. Deeply seated on the mycelium within the substance of the fos- 

 ter plant other reproductive bodies called oogonia originate. These are 

 spherical, more or less warted and brownish, the contents of which 

 become differentiated into vivacious zoospores capable, when expelled, 

 of moving in water by the aid of \ibratile cilia. A similar structure is 

 found in Cystopus candidus, a genus of the Uredines. "We shall find 

 some of the algae with active spores also. 



The fifth family is that of the Physomycetes. In these the spores are 

 produced inside of little sacs called sporangia. These sporangia are 

 borne upon threads, and each contains a number of the spores. When 

 ripe the sporangium bursts and scatters the spores. One genus grows 

 in the form of a blackened felt incrusting old wine bottles in cellars. 

 But the most interesting of this family are the Mucors (Mucorini). 

 These resemble the mucedines but differ in the method of producing the 

 spores. In some species the sporangium appears to be the result of a 

 "conjugation," or sexual union between two of the upright threads. 

 The Mucors are not parasitic on live vegetation, but only on that which 

 is dead or decaying. The Mucor Mucedo grows spontaneously in fresh 

 horse-manure if the latter be confined in a damp atmosphere under a 

 bell-glass for a few days, and will cover it all over with an ' ' immense 

 white mildew. " Growing out of the mycelium, which is spread out, are 



