GLOSSARY OF BOTANICAL TERMS 



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 (H2O) 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 -phyll) : 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 pinnae 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. -w) : That portion of 

 the ovary on which the ovules are 

 borne (fig. 56, d) ; placentae 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) cotyledonous 

 leaves, or a plant whose seedlings 



Figure 56. — A pis- 

 til : a, Stigma ; b, 

 style ; c, ovary ; d, 

 placenta bearing 

 two vertical rows 

 of ovules (rudi- 

 mentary seeds) 



