Photosynthesis (fō′tō̇-sĭn′thē̇-sĭs), the process by which green plants make sugar, starch and similar food. The materials for this are carbon dioxide and water. The former is obtained chiefly (if not exclusively) by the leaves and twigs from the air, where it constitutes three parts in 10,000. It passes through the stomata by diffusion, dissolves in the water, saturating the cell-walls, and so enters the cells. The organs by which the food is made are the minute, green bodies called chloroplasts or chlorophyll bodies, which give the plant its color. They are composed of protoplasm, which holds a green dye, chlorophyll, and are imbedded in the colorless protoplasm of those cells which lie near the surface of a plant. The chlorophyll absorbs some of the light, especially the red and yellow parts, and this energy is used (how is unknown) in the process of food-making. Even twilight (not moonlight) suffices for some photosynthesis; the amount of food made is proportional, other things being equal, to the brightness of the light. The details of the process are not known. Usually a sugar appears as the end product; this increases to a certain amount in the water of the cell; some of it is turned into starch, minute granules being formed in the chloroplasts. The food is constantly being carried away to places of use or storage. In daylight food is usually produced more rapidly than it can be disposed of; but, as photosynthesis ceases at night, the surplus is then removed. See Aëration, Chlorophyll and Stomata.
Phototaxis (fō-tō-tăks′ĭs) (in plants), the sensitiveness of an organism, free to move about, to unequal illumination (see Irritability), to which it responds by taking up a definite attitude with respect to the direction from which the brighter light acts. Only water-plants are free to respond. Diatoms, desmids, some filamentous algæ and zoöspores of algas and fungi show these reactions. Algal zoöspores swim toward light, and fungous zoöspores swim away from it.
Phrenol′ogy In popular language phrenology may be defined as the theory of mental philosophy based on the size or the relative size of the different parts of the brain. It claims that we can localize the different parts of the brain which gives rise to different mental functions. Phrenologists make a map of the cranium, on one division writing self-esteem; on another, wit; and so on. Examining your head, the phrenologist will put his finger on one point and say: “This man has a large development of self-esteem.” Moving his hand to another bump: “This man is lacking in veneration;” or “He has a great power of language;” or “He has to try hard to give exact statements;” and so on. The cultivated phrenologist thus goes through all the divisions of mental and moral qualities, finding a local boundary in the brain for each. In Britain, Gall, Spurzheim and George and Andrew Combe may be mentioned as representative phrenologists. In America the more noted ones are Dr. Charles Caldwell, the Fowler brothers and Wells.
Phryg′ia, an ancient country of Asia Minor, whose boundaries varied at different periods. It is supposed that at one time Phrygia included most of the peninsula. In general it is a high plateau which afforded pasturage for flocks. Gold was found in the mountains and streams. Vines were cultivated in some districts, and Phrygian marble was greatly prized. Phrygia was conquered by Crœsus in the 6th century and by the Persians in 549. The influence of the Phrygian religion is traced in Greek mythology.
Phycomycetes (fi′kō̇-mī̇-sē′tēz), plants
forming one of the great groups of fungi,
which is distinguished by being more like
the algæ in structure and reproductive
habits than any of the fungus groups. The
Mould, showing mycelium (m), young sporangia (g), and fertilized egg (z).
name means alga-like fungi. The mycelium
is composed of cœnocytic threads or hyphæ,
that is, filaments which contain no
partitions. (See Cœnocyte). It seems to be
more than probable that the group has been
derived from the green algæ. Prominent
members of the group are Saprolegnia
forms known as water-moulds because they
live upon the dead bodies of water-plants
