28 



MISC. PUBLICATION 110, U. S. DEPT. OF AGRICULTURE 



are of that sort. Thus, most pines 

 are polycotyledons. 



Polygamous: Having both perfect and 

 unisexual, or imperfect (i. e., either 

 staminate or pistillate) flowers 

 borne on the same individual as, for 

 example, in certain species of maple. 



Polypetalous : Having the petals dis- 

 tinct (choripetalous), and especially 

 if numerous ; the opposite of gamo- 

 petalous. 



Polysepalous : Having the sepals dis- 

 tinct (chorisepalous), and especially 

 if numerous; the opposite of gamo- 

 sepalous. 



Pome: The fleshy, applelike fruit of a 

 member of the apple family (Mala- 

 cese) ; an apple; also, though less 

 exactly, a rose hip or haw or other 

 smaller fruit of somewhat similar 

 character of the rose family. 



Figure 57. — a, Plumose 

 pappus bristles at apex 

 of b, the beaked fruit 

 (achene) of salsify, or 

 vegetable-oyster (Trcgo- 

 pogon porrifolius) 



Prickle: A sharp, pointed emergence 

 from the bark and readily pulling 

 off with it, as a rose prickle. Spines 

 or thorns partake of the nature of 

 branches or twigs and are more 

 deeply seated than prickles. 



Process: A projection or emergence, 

 usually small, from the edge or sur- 

 face, as the spiny processes on the 

 leaf margins of agaves. 



Procumbent: Lying on the surface of 

 the ground, even from the first, said 

 especially of stems. Same as pros- 

 trate. 



Proliferation: The production of new 

 parts rapidly and repeatedly from 

 buds, offsets, etc.; rapid succession 

 of cell division or a new growth so 

 formed. 



Proliferous: Reproducing freely by 

 vegetative means, as, for example, 

 offsets or buds; developing leafy 

 shoots from a flower or flower head, 

 etc. 



Prosenchyma: Vascular tissue com- 

 posed of elongated, mostly thick- 



walled, fibrous, pointed cells, with- 

 out intercellular spaces; one of the 

 two general types of tissue in the 

 higher plants, the other being the 

 parenchyma. 



Prostrate : Lying on the surface of the 

 ground, even from the first; said 

 especially of stems. Same as pro- 

 cumbent. 



Prothallium (pi. -ia) : The same as 

 prothallus. 



Prothallus : The sexual stage or gener- 

 ation (gametophyte) of ferns and 

 related cryptogams ; it consists of a 

 small, usually flat and green body 

 (thallus) attached to the ground or 

 other growing surface by rootlets 

 (rhizoids) on the under surface, and 

 bears the male and female organs 

 (antheridia and archegonia) either 

 on the same or on separate plants. 

 See alternation of generations. 



Protoplasm: The colorless, semifluid, 

 highly complex, nitrogenous (pro- 

 teid) material found in all living 

 tissue, both plant and animal, and 

 which is the physical basis of life. 



Pruinose: Beset, as if dusted, with a 

 white, frostlike bloom, or indument, 

 of fine vegetable wax, as, for exam- 

 ple, on the stems and leaves of cer- 

 tain crucifers, on certain berries and 

 other fruits, etc. Glaucous to an 

 extreme degree. (Latin pruina, 

 hoarfrost.) 



Pseudo-: A prefix (Greek) signifying 

 false. 



Pteridophyte : A fern or fern ally. A 

 member of the natural group (phy- 

 lum) Pteridophyta, consisting of the 

 various orders and families of ferns, 

 horsetails, clubmosses, quillworts, 

 and other of the higher nonflowering 

 plants, or cryptogams; the vascular 

 cryptogam of the older botanists. 

 Save for the tree ferns of the Trop- 

 ics all living pteridophytes are 

 herbs. 



Puberulent: Very finely pubescent 



Pubescent: In current botanical usage 

 a general term meaning hairy ; spe- 

 cifically, however, the term means 

 downy haired ; covered with fine, 

 soft short hairs (pubescence). 



Pulvinate: Resembling a cushion. 



Pulvinus: A cushionlike appendage, as 

 the hairy pulvini in the axils of the 

 inflorescence branches of beard- 

 cushion witchgrass (Panicum ~bar- 

 tipulvinatum) . 



Punctate: Dotted, especially if beset 

 with minute holes or depressions, 

 as the small translucent glands in 

 the leaves of St. Johnswort (Hyper- 

 icum). Sometimes used as a syno- 

 nym of minutely papillate, i. e., be- 



