GLOSSARY 249 



Oosphere (egg sphere). An egg cell. 



Oospore (egg spore). A fertilized o.gg which develops a heavy w;ill and 



passes through a [leriod of rest before gerniinaling. 

 Open bundle. A Hbro-vascular bundle which contains cambiiini and 's 



consecpiently capable of further growth. 

 Operculum, plu. opercula (a cover). In mosses the cover of the spore case. 

 Order. A taxononiic group composed of families. 

 Osmosis (a thrusting). The diffusion or interchange of licjuids through 



membranes. 

 Ovary. The ovule-bearing part of the pistil. 

 Ovule. The undeveloped structure which after fertilization becomes the 



seed. 



Palisade cells. Elongated parenchyma cells of a leaf, which lie beneatl 



the epidermis with their long axes at right angles to the leaf surface 

 Palmate (like the palm of the hand). AVith veins or sinuses radiating 



like fingers. 

 Parasite. An animal or plant that obtains its food from some other liv- 

 ing organism, called its host. 

 Parenchyma. Tissue composed of nearly globular cells or polyhedral 



cells the diameters of which are approximately equal, as pitli. 

 Parietal (a house wall). Pertaining to a wall, as a placenta on an ovary 



wall. 

 Parthenogenesis (virgin generation). The development of an i^gg or 



other gamete without the process of fertilization. 

 Pathogenic (disease offspring). Producing disease. 

 Pedicel (a little foot). The stalk on which an organ is borne, esjiecially 



the flower stalk of each separate flower in a cluster. 

 Peduncle (a little foot). The flower stalk. 

 Perianth (around the flower). A collective term for calyx and corolla 



taken together. 

 Periblem (clothing). The part of the meristem at the growing apex of 



a root or shoot, immediately beneath the epidermis. It develops 



into the cortex. 

 Pericambium. See Pericycle. 



Pericycle. The outermost layer of the central cylinder of a root. 

 Perigynous. A term applied to those flowers in which the stamens and 



perianth appear to grow from around the wall of the ovary. 

 Peristome (around the mouth). In mosses the circle of teeth or .segmenta 



surrounding the opening of the spore case. 

 Perithecium (around a case). In sac fungi, Ascomycctcs (including 



lichens), a cavity containing the sacs or asci. 

 Petal (a flower leaf). A leaf of the corolla. 

 Petiole (a little foot). A leaf stalk. 

 Phloem (bark). The soft portion of a fibro-vascular bundle, — the bast. 



In dicotyledons the part outside of the cand)ium, — the inner i>ark. 

 Photosynthesis (light putting together). Th«' process of manufacture of 



carbohydrates, such as starch and sugar, fnun water antl carbon 



