AN ENCYCLOPAEDIA OF HORTICULTURE. 



161 



FIiEIOS. A term which, used in Greek compounds, 

 signifies more than one ; e.g., Pleiophyllus, several- 

 leaved. 



FLENTJS. Pnll; double. Applied to flowers in 

 which the number of petals, &c., is abnormally multi- 

 plied. 



FLEOCNEMIA. Included under Nephrodinm 

 (which see). 



FLEOMELE. A synonym of Dracaena (which see). 

 FLEOMORPHISM. See Pleomorphy. 



FLEOMORPHY, or PLEOMORPHISM (from 

 pleion, several, and morphe, form; in allusion to. the 

 variability in the spores). A term used to express 

 the condition observed in several groups of Fungi (see 

 Oidium, Feronospora, Fleospora, Pnccinia, and 

 Pyrenomycetes), in which bodies of two or more forms 

 are produced to effect reproduction of these plants under 

 varying conditions; one form is, in some groups, known 

 to be the result of sexual reproduction, e.g., zygospores 

 of Peronospora, ascospores of Peziza and Pyrenomycetes, 

 &c., and to such the term " spore " is, by some botanists, 

 restricted in theory, though this is scarcely adhered to 

 in practice. All the other forms of bodies specialised 

 for reproduction fall under the two types of conidia 

 and sclerotia. In many plants, conidia of two or more 

 kinds occur, either simultaneously or in succession, and 

 in many Fungi (e.g., Hymenomycetes, Pucciniei, &c.) no 

 sexual form has yet been detected. 



FLEOFELTIS. Included under Polypodiiun 

 (which see). 



PLEOSPOK.A. A genus of parasitic Fungi, belong- 

 ing to the group of Pyrenomycetes, and to the sub-group 

 SphteriacecB, in which the perithecia are globular or 

 flask-shaped, and open by a circular pore or mouth to 

 permit the escape of the spores. The perithecia are 

 borne upon a mycelium, which penetrates the tissues of 

 the host- plant ; but they are quite separable from this 

 mycelium. The genus is one of a section in which the 

 perithecia are at first covered by the epidermis of the 

 host-plant, through which, usually, they ultimately burst. 

 The mycelium does not form an evident layer or mas? 

 (stroma). The perithecia are not very thick- walled, are 

 dark brown, and generally smooth ; the opening, or neck, 

 usually projects from the stratum in which the bodies 

 are sunk. Another form of spore (conidia) is usually 

 produced on the surface on the same host. The spores 

 produced in the asci, inside the perithecia, are divided 

 by numerous cell-walls, crosswise and lengthwise, so as 

 to resemble the arrangement of bricks in a wall, and 

 they are usually some shade of brown, seldom colour- 

 less. A number of species of Pleospora exist, some 

 parasitic on one plant, some on another; but most of 

 them seem to be found in the perfect condition only on 

 dead or dying stems and leaves, and are thus, in this 

 stage, not hurtful to garden or field produce. A large 

 proportion of the species have been found only on wild 

 plants or on grasses; and there is considerable doubt 

 as to the number of really distinct species, since many 

 of the named forms are only varieties of the extremely 

 common P. herbarum. It will be well to give here a 

 brief description of the conclusions of mycologists with 

 regard to the life-history of this species, as it is believed 

 to be injurious to various garden plants in its earlier 

 conditions; and several of these stages differ so much 

 from one another, and from the mature condition, that 

 they have been described as distinct species under widely- 

 separated groups. This Fungus is supposed to be the 

 cause of a disease of Potato-plants, characterised by 

 retardation of growth and curling of the leaves, which 

 become yellowish-green. On the leaf-stalks and stems 

 there appear brown spots, at first round, but widening 



Fleospora continued. 



out, and, after a time, the whole stalk, with its leaves, 

 withers and dies. The formation of tubers is but small. 

 Various other garden and field plants, and many wild 

 plants, present diseased conditions that are generally 

 referred to the action of P. herbarum. Some botanists 

 are of opinion that experimental researches, by means of 

 cultivation of the Fungus, show that two distinct species 

 have been confounded under the name P. herbarum, and 

 that these two can be distinguished in the earlier, though 

 not easily, if at all, in the mature, state ; and they have 

 been named, by Gibelli, P. Sarcinulas and P. Alternarias. 

 Practically, to gardeners, it matters little whether there 

 are two species or only one, as both forms are common, 

 and they agree in the mode of life. 



The Fungus can seldom, if ever, be observed in plants of 

 quite a healthy appearance ; but it undoubtedly exerts its 

 action some time before it is externally visible, and, in this 

 period, the food-plant becomes penetrated by its colourless, 

 branched mycelium. On this mycelium, near and on the 

 surface of the plant, are formed the reproductive organs, 

 in the form of conidia of two or three kinds, succeeded by 

 the pycnidia and the perithecia. Both the latter are 

 globular or flask-shaped bodies, with a narrowed neck, and 

 a membranous, leathery or brittle, cellular coat. They 

 are usually scattered plentifully on the surface of dead 

 stems and leaves. The pycnidia are full of minute, 



FIG. 201. PI.EOSPORA HERBARUM, PYCMUIAL STAGE (known as 

 Phoma herbarum) a, Pycnidia in transverse section, x 20, one 

 opened ; 6, Conidia still on the Stalks, x 400 ; c, Conidia free 

 after falling off the Stalks, x 400. 



elliptical, transparent, one-celled bodies (see Fig. 201), 

 borne on slender stalks from the inner surface of the 

 | walls. The perithecia are larger and darker than the 

 ! pycnidia, and differ from these in the spores contained 

 j in them being inclosed in large, transparent, elongated, 

 I cells (asci). In each of these are eight spores (se 



X20 



x200 



FIG. 202. PLEOSPORA HERBARUM, PERFECT STAGE, WITH ASCI 



o, Piece of Herbaceous Stem, with Perithecia, natural size ; 

 6, Section of Stem, with two Perithecia, one opened, x 20; 

 e. Unripe Ascns, x 200 ; d, Ripe Ascus, x 200, inclosing eight 

 ripe Spores; e, e, e. Three Ripe Spores, x 400, showing 

 differences in size, form, and divisions. 



Fig. 202). The latter are some shade of brown, elliptical, 

 narrowed in the middle, and show numerous partitions, 

 of which seven are across the length, and others divide 

 the spaces so formed into smaller spaces or cells. They 

 are very much larger than the spores contained in the 

 pycnidia. The conidia are formed, not in special recep- 

 tacles, as in the former cases, but exposed on the surface 

 of the plant. One of the earliest Fungi to appear on 

 sickly plants in general is a bluish or greenish-grey coat 



y 



