788 GLOSSARY. 



Periderm. The outer layers of the trunk and older branches, which are 



formed from the phellogen or cork cambium (p. 291). 

 Perigynous. Applied to a flower when the stamens are adnate with the 



tube of the perianth, as in the cherry (p. 389). 

 Peristome. The margin of teeth-like cells at the summit of certain moss 



capsules (p. 79). 

 Petiole. The stalk of a leaf. 

 Petiolule. The stalk of a leaflet. 



Phelloderm. The thin-walled parenchyma cells formed by the cork cam- 

 bium (p. 291 ). 



Phellogen. The meristem which forms cork and the phelloderm (p. 291). 

 Phloem. The leptone, stereome and accompanying cells of a fibrovascular 



bundle (pp. 312 and 341). 

 Photosynthesis. The process by which the chloroplastids, aided by light, 



manufacture starch and glucose from carbon dioxide and water (pp. 



137 and 157). 



Pileus. The cap of mushrooms (p. 57). 



Pinnae. The primary divisions of a compound leaf or frond of a fern. 

 Pinnatifid. A leaf in which the divisions extend near to the midrib, the 



lobes being narrow and acute. 

 Pistil. The structure consisting of one or more megasporophylls in the 



spermophytes, and made up of the stigma, style and the ovary, en- 

 closing the ovules. 

 Pistillate. A flower provided with megasporophylls and lacking the 



microsporophylls, as the pistillate flowers of the oak. 

 Placenta. That portion of the ovary which extends into the loculi from 



the united margins of the carpels and bears the ovules (p. 377). 

 Plumule. The rudimentary bud at the summit of the epicotyl of the 



embryo, as tonka seed. 

 Pollination. The transferral of the pollen from the anther to the stigma 



(p. 397). 

 Pollinium (Pollinia). An agglutinated mass of pollen grains as in the 



milkweed flowers. 

 Polypetalous. A flower in which the petals are separate ; applied to the 



Choripetalae or Archichlamydeae (p. 504). 

 Pome. An indehiscent, half-inferior fruit consisting of the fleshy torus, 



as in the apple (p. 420). 



Pore. An imthickened portion of a cell wall (pp. 263 and 275). 

 Procumbent. Prostrate ; as the stem of the trailing arbutus. 

 Prothallium (Prothallus). The gametophyte of the ferns (p. 88). 

 Protonema. The prothallus of the mosses (p. 78). 

 Puberulent. Covered with fine, very short hairs. 

 Pubescent. Hairy ; frequently used in a general way to denote diverse 



types of hairiness. 

 Punctate. Applied to translucent dots caused by the presence of oil 



reservoirs within the tissues, as in the leaves of pilocarpus. 

 Putamen. The hard and stone-like endocarp of the cherry and peach. 

 Pyriform. Pear-shaped. 

 Raceme. A simple inflorescence of the indeterminate type, in which the 



flowers are alternately arranged on the main axis as in the lily-of- 



the-valley (p. 394). 



Rachis (Rhachis). The axis of a raceme or spike of flowers; also ap- 

 plied to the stalk bearing the leaflets of a pinnately compound leaf. 

 Radiate. Applied to the inflorescence of the Composite, in which the 



heads consist of both tubular and ray flowers, as in the sunflower. 

 Radicle (Caulicle). A rootlet, or specifically the hypocotyl of the embryo 



in the seed. 



