GLOSSARY 249 



Oosphere (egg sphere). An egg cell. 



Oospore (egg spore). A fertilized egg which develops a heavy wall and 



passes through a period of rest before germinating. 

 Open bundle. A fibro-vascular bundle which contains cambium and is 



consequently capable of further growth. 

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

 Order. A taxonomic group composed of families. 

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



membranes. 

 Ovary. The ovule-bearing part of the pistil. 

 Ovule. The imdeveloped structure which after fertilization becomes the 



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



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

 Palmate (like the palm of the hand). With 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 pith. 

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



wail. 

 Parthenogenesis (virgin generation). The development of an egg 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, especially 



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 cylinler 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 toeth or segments 



surrounding the opening of the spore case. 

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



lichens), a cavity containing the siics 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 cambium, — the inner bark. 

 Photosynthesis (light putting together). The process of manufacture of 



carbohydrates, such as starch and sugar, from water and carbon 



