GLOSSARY OF BOTANICAL TEEMS 



27 



chlorophyll-bearing cell granules, in 

 the presence of light (normally sun- 

 light) and usually in the leaf. The 

 starch is gradually derived from 

 water and carbon dioxide. The 

 water (H 2 0) is obtained from the 

 soil by means of the root hairs on 

 the roots, and carbon dioxide (C0 2 ) 

 is absorbed from the air through the 

 stomata. In the process of photo- 

 synthesis free oxygen (O) is given 

 off through the stomata, and this is 

 the scientific basis for the popular 

 dictum that plants purify the air. 



Phototropism: The common phenome- 

 non exhibited by plants or their or- 

 gans in growing toward or turning 

 to a source of light. Heliotropism 

 (turning toward the sun) is prac- 

 tically synonymous with phototrop- 

 ism, though similar tropisms can be 

 induced by artificial light. 



Phyllary: One of the (often sepallike) 

 involucral bracts subtending the 

 flower head of a composite. 



Phyllo- (or -pliyll) : An element 

 (Greek) in compound words signify- 

 ing leaf. 



Phylogeny: The life history, evolution, 

 or genetic relationship of a group 

 (as an order, family, genus, species, 

 or race) of plants or animals, as dis- 

 tinguished from ontogeny, which 

 concerns the study of an individual 

 plant or animal. 



Physiology: The branch of biology 

 which deals with life processes and 

 functions. Plant physiology is the 

 study of how plants grow and repro- 

 duce and of the varied functions of 

 their organs or other parts. 



Pilose: Hairy with soft slender hairs. 



Figure 55. — Pinnate leaves : A, Odd- 

 pinnate leaf of vetch (Vicia), with 

 the terminal leaflet represented by a 

 tendril ; B, even-pinnate leaf, as in 

 Cassia 



Pinna (pi. -ae) : A main or primary 

 division of a pinnate leaf, a single 

 leaflet if the leaf be simply or once 

 pinnate. Each of the leaflets shown 

 in Figure 55 is a pinna ; each of the 



main divisions in the bipinnate leaf 

 shown in Figure 12 is a pinna; its 

 individual leaflets are pinnules. 



Pinnate: Having the parts (usually 

 said of leaves) arranged on each side 

 of a common axis ; a compound leaf 

 with opposite leaflets (fig. 55, A, B), 

 as in ashes or peavines, is pinnate. 



Pinnatifid: Pinnately or oppositely 

 (featherwise) cleft or parted almost 

 to the midrib, or else lobed to the 

 middle. (Figs. 13, 18, 40 B, and 

 50.) Approaching pinnate. 



Pinnule: An ultimate leaf division, or 

 leaflet, of a bipinnate leaf (fig. 12) ; 

 the main division of a pinna. In a 

 thrice pinnate leaf the pinnse would 

 be divided into pinnules and each of 

 the pinnules, in turn, would be pin- 

 nately divided into leaflets. 



Pistil: The female or seed-producing 

 organ of a flower, consisting typi- 

 cally of ovary, 

 style, and stig- 

 ma (fig. 56), 

 the style, how- 

 ever sometimes 

 wanting. 



Pistillate: Fe- 

 male ; bearing 

 pistils or seed- 

 producing or- 

 gans only. Said 

 of flowers 

 which are pro- 

 vided with pis- 

 tils but not 

 with stamens, 

 and of individ- 

 ual inflorescences and plants having 

 only pistillate flowers. Expressed 

 by the symbol $ (Venus's-looking- 

 glass). 



Placenta (pi. -ce) : That portion of 

 the ovary on which the ovules are 

 borne (fig. 56, d) ; placentse of sim- 

 ple pistils are marginal and, com- 

 pound pistils, usually axile, parietal, 

 or basal. 



Plumose: Feathery or featherlike; hav- 

 ing fine hairs on each side, like the 

 plume of a feather. (Fig. 57, a.) 



Plumule: The little, often featherlike 

 bud, at the summit of the radicle in 

 an embryo or germinating seedling, 

 situated between the two cotyledons 

 in a dicotyledonous plant, and from 

 which the mature plant stem and 

 leaves eventually develop. 



Pollen: The fertilizing floral dust or 

 powder; fecundating granules de- 

 veloped within the anther. 



Poly-: A Greek prefiix meaning many. 



Polycotyledon: A seedling with numer- 

 ous (at least three) cotyledonoiis 

 leaves, or a plant whose seedlings 



Figure 56. — A pis- 

 til : a, Stigma ; 6, 

 style ; 0, ovary ; d, 

 placenta bearing 

 two vertical rows 

 of ovules (rudi- 

 mentary seeds) 



