440 PLANT MORPHOLOGY 



Pollen tube. The tube produced by a pollen grain when it germinates. 



Pollination. In angiosperms, the transfer of pollen from a stamen to a pistil or, in 

 gymnosperms, to an ovule. 



PoUinium. A mass of coherent pollen grains, as in milkweeds and orchids. 



Polycotyledonous. Having many cotyledons, at least more than two. 



Polyembryonous. Having several embryos in the same seed. 



Polymerous. Having many floral parts in each set. 



Polyphyletic. Derived from more than one ancestral stock. 



Polyploid. Having several or many times the basic or haploid chromosome number. 



Polysiphonous. Consisting of several or many united filaments, as the plant body of 

 certain brown and red algae. 



Primary xylem. Wood differentiated directly from a terminal meristem and consist- 

 ing of protoxylem and metaxylem. 



Primordium. A rudiment or first-formed part of an organ or member. 



Procarp. The female sex organ of the red algae, consisting of a carpogonium and a 

 trichogyne. 



Proembryo. In pteridophytes and spermatophytes, a group of cells derived from the 

 fertilized egg and later differentiating into a suspensor and embryo. 



Prothallium. The reduced, thalloid gametophyte of the pteridophytes. 



Protonema. The primary or filamentous stage in the development of a moss gameto- 

 phyte. 



Protostele. A solid stele, without a central pith. 



Protoxylem. The first xylem to be formed in an organ. 



Pseudopodium. A temporary foot-like protrusion of an amoeboid cell, used in loco- 

 motion and in the procuring of food. In Sphagnum and Andreaea, a leafless 

 stalk developed from the stem of the gametophyte in which the foot of the sporo- 

 phyte is embedded. 



Pyrenoid. A starch-forming body in the chloroplast of many algae. 



Pyriform. Pear-shaped. 



Rachis. In divided ("compound") leaves, the extension of the petiole bearing the 

 leaflets. 



Radial. Occupying alternate radii, as the arrangement of primary xylem and phloem 

 in a root. 



Radicle. The rudimentary root in the embryo of a seed plant. 



Ramentum. A woolly covering of scales on the stem, as in many ferns. 



Raphe. In anatropous ovules, the portion of the funiculus that is united to the integu- 

 ment, forming a ridge along the body of the ovule. In diatoms, a longitudinal 

 slit extending along the median line of a valve. 



Receptacle. In liverworts, a special branch or portion of the thallus that bears the 

 sex organs. In angiosperms, the portion of the axis that bears the floral parts. 



Regular flower. One in which the members of each whorl of perianth parts are 

 uniform in size and form. 



Reticulate. Forming or resembling a network. 



Rhizoid. In the lower plants, one of the root-like filaments that attaches the game- 

 tophyte to the substratum. 



Rhizome. An elongated underground stem; a rootstock. 



Rhizophore. A special root-bearing organ. 



Rootcap. A cellular sheath at the end of a root tip. 



Saprophyte. A plant living on dead organic matter. 



Scalariform. Ladder-like; having bars or markings like the rungs of a ladder. 



