GLOSSARY 377 



Phyllotaxis. Leaf-arrangement: alternate, or separate in 2, 

 3, 5 or 8 ranks, on many plants; opposite, or in groups 

 of 2, in others; whorled, or in groups of more than 2, in 

 still others. 



Physiology. The science of function in living things, classi- 

 fying their parts as organs with respect to the work they 

 perform. Organs of unlike morphological origin are anal- 

 ogous to one another. See metamorphosis; morphology. 



Pinna. One of the divisions of a pinnate leaf. 



Pinnate. Like the plume of a feather: having the leaflets 

 along a rachis, as applied to compound leaves (tamarind). 

 Contrasted with digitate or palmate. 



Pinnule. A leaflet of a bipinnate or decompound leaf. 



Pistillate. Producing pistil, or seed-organ, but not stamens 

 (ear of corn, "female" cottonwood). 



Pith. The central part of a dicotyledonous or exogenous 

 stem, surrounded by the woody cylinder: usually continu- 

 ous and of uniform texture, or gritty or surrounded by 

 cells different from those at the center, or exceptionally 

 with plates of firmer cells, or diaphragms, at the nodes 

 (paper mulberry, grape) or at intervals between them 

 (tupelo) though otherwise continuous; rather commonly 

 with cavities like a sponge (evonymus), or entirely exca- 

 vated or disappearing, at least between the nodes (honey- 

 suckle) so as to make the stem fistulous; not infrequently 

 chambered between persistent thin plates or disks (wal- 

 nut) when it is spoken of sometimes as discoid. 



Pithy. Sometimes used in the sense of having large pith 

 and little wood. 



Pod. A dry dehiscent seed-vessel. 



Pointed. The general equivalent of acute, acuminate or mu- 

 cronate. 



Pollen. The male cells or microspores produced by flowers. 



Pome. An apple-fruit, with a papery or bony core at center 

 and crowned by sepals or scars from which they have 



