256 



THE DICTIONARY OF GARDENING, 



Pyrenomycetes continued. 



in most, these groups of asci are surrounded with an 

 outer coating of hyphse, united so as to simulate true 

 parenchyma. In one group tb Discomycetes this pro- 

 tecting tissue merely forms a saucer or disk, or a club, 

 on which the asci stand (e.g., in Peziza), and the surface 

 bearing the asoi is exposed. In a few, e.g., Exoascu\ 

 Pruni (see remarks on FUNGI, under Plum), the asci 

 stand isolated and exposed, and not on any special area 

 of the surface. In the Pyrenomycetes, including among 

 them the Perisporacei, the protecting tissue forms a 

 continuous sphere or flask- shaped perithecium, which 

 entirely incloses the asci with the spores in them, and 

 which, as in the Perisporiacece, may be entirely closed, but 

 far more generally opens by a pore or slit on its upper 

 surface, or at the end of a more or less elongated neck. 

 As a rule, there are many asci in each perithecinm ; but 

 in a few species they may be few, or even reduced to 

 a single ascns, as in Podosphcera (see PLUM FUNGI). 

 Both in Discomycetes and in simple Pyrenomycetes, the 

 development of the asci and spores has been traced to 

 a union of male and female organs, and the protecting 

 layers have been traced to branches developed from the 

 mycelium after the female cell is fertilised. 



Fio. 330. Two ASCI OF PEZIZA POSTHMA, each with eight Spores 

 (magnified about 250 times). 



The Pyrenomycetes live on every kind of food on dead 

 wood and leaves, on dead animal matter, on excrements, 

 on the soil, and on living plants and animals; in this 

 latter case, they are true parasites. Some of them prove 

 hurtful to cultivated plants. An account of the more 

 important structural characters of the Erisyphece, and 

 of the injuries they inflict, will be found under the 

 headings Mildew and Oidium. The restricted, or 

 true, Pyrenomycetes differ from the Perisporiacece (of 

 which the Erisyphece form the section of most import- 

 ance to gardeners) in the perithecium opening by a pore 

 or a slit, and in the mycelium being not superficial, but 

 sunk among the food, whether that is dead, or a living 

 plant or animal. Hence, the mycelium is entirely con- 

 cealed ; and the parts which ' attract our notice are, 

 in most cases, only the reproductive organs. There 

 are several kinds of spores produced, as has been 

 mentioned under Pleospora. The ascospores, or 

 those contained in the asci, may be round, elliptical, 

 or thread-like, transparent or brown, undivided, or 

 divided by one, two, three, or many septa. In 

 this latter case, the spores often seem very complex 

 in their structure, being built up of many cells. The 

 perithecia vary considerably in texture, whether nearly 

 membranous, carbonaceous, or fleshy (Nectriacece), and in 

 form of orifice, whether a simple slit (in Hysteriacei), or 

 a pore (Pleospora), or with thickened lips (Lophiosto- 

 macei). In some, the perithecia are scattered (Pleospora) ; 

 in others, they are crowded together on specially modi- 

 fied parts of the Fungus (in Xylaria, Claviceps, &c.), or 

 are sunk in the mycelium, in a mass called a " stroma." 

 Besides the perithecia with ascospores, other structures, 

 called pycnidia, much like perithecia in external appear- 



Pyrenomycetes continued. 



ance, are developed ; and in them are contained spores, 

 often much like those contained in the asci, e.g., in 

 Cucurbitaria Laburni, where both are mnltioellnlar and 

 brown, but, perhaps, more often very different from them 

 in appearance, e.g., in Pleospora herbarum, in which the 

 ascospores are multicellnlar and brown, and the pycnidio- 

 spores are unicellular, transparent, and very much smaller 

 (see Pleospora). The pycnidia have been named Phoma 

 herbarum. Pycnidia are, in most cases, smaller and 

 thinner-walled than the perithecia ; but they vary in 

 these respects, and also in being solitary in some groups, 

 and crowded together in others. Occasionally, they are 

 sunk in a stroma. They usually occur on the mycelium 

 before the perithecia are formed, but may be associated 

 with the latter. In the pycnidia, the spores are pro- 

 duced on the tips of branches, not in asci; but 

 pycnidiospores are occasionally found in the same re- 

 ceptacle with ascospores. 



Other modes of spore formation occur in many species 

 (see Fleospora), resulting in the formation of conidia on 

 the tips of branches that rise from the mycelium creeping 

 on the surface of the body in which the Fungus is 

 growing. These conidiophores, or conidia-bcarers, are 

 very various in form and modes of branching, and in the 

 structure and form of their spores. In some cases, they 

 are so associated with the more perfect stages of the 

 Fungi that there is little difficulty in recognising their 

 relationships ; e.g., the very common Tubercularia vulgaris 

 on dead branches is always followed by Nectria cinna- 

 barina in such a manner as to indicate clearly their 

 being states of the same Fungus. But the greater 

 number of conidiophorons Fungi have not yet been 

 referred as earlier stages to higher forms, though careful 

 observations will almost certainly result in their being 

 so, and will free the study of microscopic Fungi from a 

 vast amount of doubt, and from multitudes of so-called 

 species. In the meantime, in the imperfect state of our 

 knowledge of these plants, it is found expedient to 

 retain them in the group called Hyphomycetes, even 

 though they are thus associated with Peronospora, and 

 with other forms not closely related to them. Still 

 another mode of reproduction in some is by means of 

 Sclerotia, or hard masses of mycelium (see Sclerotia). 

 It has been necessary to enter thus fully upon the 

 account of the modes of reproduction observed in the 

 Pyrenomycetes, since it is these alone that afford 

 material for distinguishing the various genera and 

 species, the mycelium not yielding characters that can 

 be relied on for genera, or even families, much less for 

 species. For an account of the injuries inflicted on 

 cultivated plants by the Erisyphece among Perisporiacei, 

 see Mildew and Oidium. Among the restricted Pyre- 

 nomycetes, a good many species are parasitic upon 

 living plants ; and several of these are injurious to field 

 or to garden produce. Some of them are hurtful in the 

 early stages of their growth, the perithecia being 

 formed only after the death of the tissues on which 

 they feed. Others only weaken the host-plants, and are 

 to be found in all their stages upon living tissues of 

 these plants. Some have already been referred to under 

 the headings Pleospora and Plum (FuNGi). Among 

 the most injurious forms may be mentioned one very 

 hurtful to grasses that are grown for seed, viz., the 

 Ergot (Claviceps purpurea), which, however, does so 

 little harm to gardeners as to require no special notice 

 here. 



PYBETHRUM (Pyrethron, the old Greek name used 

 by Dioscorides, probably from pyr, fire ; referring to the 

 acrid roots of this genus). Feverfew. OBD. Composites. 

 A genus of mostly hardy, herbaceous perennials, now in- 

 cluded, by Bentham and Hooker, under Chrysanthemum. 

 " The distinctive features reside in the presence in Pyre- 

 thrum of a pappus, in the form of an elevated membranous 



