EXPLANATION OF TERMS. 



Oospore. Immediate product of ferti- 

 lisation in oosphere. 



Operculum. In Musci : lid of capsule. 



Opposite. In a flower : same as super- 

 posed. 



Orthotropous. An ovule of which the 

 nucellus is straight and appears as a pro- 

 longation, in the same straight line, of 

 the funiculus is orthotropous. Same as 

 straight. 



Ovary. That part in a flower which con- 

 tains the ovules. 



Ovule. In Phanerogams: macrosporangium 

 consisting of a body or nucellus with or 

 without one or two integuments (primine 

 and secundine) and containing one macro- 

 spore, the embryo-sac. 



Palea. (a] In Filices : a flat outgrowth of 

 the epidermis composed of one or several 

 layers of cells and attached at one side, 

 i. e. a scale-hair attached laterally. Same 

 as chaff-scale and ramentum. (b) In 

 Gramineae : an inner bract subtending 

 one flower. 



Panicle. A twice or more branched race- 

 mose monopodial inflorescence with the 

 primary branches at least elongated. 

 Pappus. In Compositae : tuft or circle of 

 hairs or scales developed at the summit of 

 the inferior achene. 

 Parallel chorisis. See chorisis. 

 Paraphyses. Sterile unicellular or pluri- 

 cellular filaments or narrow plates accom- 

 panying sporogenous or sexual organs ; 

 in Fungi : with asci or basidia in hyme- 

 nium ; in Muscineae : with antheridia 

 and archegonia ; in Filices : with spo- 

 rangia in a sorus. 



Parasite. An organism living on or in and 



at the expense of another organism (host). 



Parthenogenesis. Form of apogamy in 



which the oosphere (ovum) developes into 



the normal product of fertilisation without 



a preceding sexual act. 



Pedicel. Stalk of a flower as an ultimate 



branch of inflorescence. 

 Peduncle. Stalk of a flower. 

 Peltate. A leaf is peltate when the lamina 

 is expanded at right angles to the petiole 

 in such a way that the petiole is attached 

 to the lower surface. 



Penicillate. Having the form of a pencil 

 of hairs. Used in this book erroneously 

 as equivalent to feathery. 

 Pentacyclic. A flower with five whorls of 



members is pentacyclic. 

 Pentamerous. A flower in which calyx, 

 corolla and androecium have each five 

 (or a multiple of five) members is pen- 

 tamerous. 



Perianth. Floral envelope composed of 

 calyx and corolla or of calyx alone. 



Periblem. Meristematic zone lying be- 

 tween the plerome and dermatogen 

 in a growing point. Same as primary 

 cortex. 



Pericarp. Wall of an ovary developed 

 into fruit. 



Perichaetium. In Muscineae : envelope 

 of leaves surrounding a group of anthe- 

 ridia and archegonia or of archegonia 

 alone. 



Periclinal. 



Running: in the same direction 



with the circumference of a part. Comp. 

 anticlinal. 



Periderm. The cork-cambium and its 

 products. This is the sense in which 

 De Bary uses the term and is an extension 

 of its original signification. 

 Peridiola. In Gasteromycetes : nests of 

 tissue within the 'fructification' inside 

 which the hymenium is formed. 

 Peridium. In Angiocarpous Fungi : outer 

 envelope forming a complete investment 

 of the 'fructification.' 

 Perigonium. In Musci : envelope of leaves 



surrounding a group of antheridia. 

 Perigynium. In Hepaticae : special en- 

 velope of the archegonia. 

 Perigynous. Inserted on a cup of the 

 torus around an ovary. Comp. hypo- 

 gynous, epigynous. 



Periplasrn. In Peronosporeae: protoplasm 

 in the oogonium and the antheridium 

 which does not share in the conjugation. 

 Comp. gonoplasm. 



Perisperm. Tissue filled with nutrient 

 material in the seed derived from the 

 nucellus and therefore outside the em- 

 bryo-sac. Comp. endosperm. 

 Peristome. In Musci : series of teeth 



round mouth of open capsule. 

 Perithecium. Cup-shaped ascocarp with 

 the margin incurved so as to form a 

 narrow mouthed cavity. Same as pyreno- 

 carp ; used also in this book in sense of 

 cleistocarp. 



Perizonium. In Diatomaceae : thin 

 non-silicious membrane of a young auxo- 

 spore. 



Petal. Leaf of corolla. 

 Petaloid. Like a petal. 

 Petiole. Stalk of leaf. 

 Phloem. Region of a vascular bundle or of 

 an axis with secondary thickening which 

 contains sieve-tubes. Comp. xylem. 

 Phylloclade. Branch resembling a leaf. 

 Same as cladode and cladophyll, but 

 these latter are properly restricted to 

 branches of one internode. 

 Phyllody. Substitution of a foliage leaf 

 for the normal organ. Same as phyllo- 

 morphy and frondescence. 

 Phyllomorphy. Same as phyllody. 

 Phyllopodium. A leaf regarded morpho- 



