PHYLLOCLAD
1480
PHYSICAL EDUCATION
and animals, sometimes attacking living fish, one species being very destructive to fish in hatcheries. It is interesting to note that this group of fungi has retained the aquatic habit of the algse. As a consequence, its asexual spores are ciliated and have the power of swimming. Another feature of the water-moulds is that the oOgonium sometimes forms several eggs and that frequently the eggs form new plants without any fertilization, being an illustration of the habit called parthenogenesis (which see). The mucor forms are well-represented by the black moulds, which form white, furry growths on damp bread, manure-heaps etc. From the prostrate mycelium arise numerous erect branches, each bearing at its summit a globular sporangium containing numerous asexual spores. The mucors are isogamous (which see). The peronospora forms are the downy mildews which are common internal parasites on seed-plants, one of the most common kinds attacking grape leaves. The presence of the parasite is made known by discolored and finally deadened spots on the leaves where the tissues have been killed. The spore-bearing branches rise above the surface of the leaf, and, many of them arising near together, form little velvety patches suggesting the name downy mildew. These forms are heterogamous. See HETEROGAMY.
Phyl'loclad (in plants). See CLADOPHYLL.
Phyllodia (fl-lo1'd/i-a}, (in plants), petioles which resemble leaves in form and function. The most conspicuous display of phyllodia is among the acacias, especially hose of Australia. The normal leaves are pinnately compound, but for the most part they do not develop, the petiole becoming flat and doing the leaf work.
Phyllotaxy (ftl'M-t&ks'y). The name literally means leaf-arrangement, and has to do with the distribution of leaves upon the stem and the laws which govern it. In general, there are two types of leaf arrangement : that in which the two or more leaves are developed at the same node, giving rise to what is called the yerticillate or cyclic arrangement; and that in which but a single leaf occurs at each node, giving rise to the alternate or spiral arrangement. In the case of the spiral arrangement some relations have been discovered which seem to be more curious than important. In the simplest cases the leaves occur in two vertical rows, the angular divergence between any two successive leaves being half of the circumference of the stem or 180°. This type of phyllotaxy is designated by the fraction J, which shows the angular divergence, while the denominator indicates the number of vertical ranks. In the next higher series the leaves occur in three rows, the angular divergence between successive leaves being one third the circumference or 120°. The fraction f designates this arrangement.
The next higher arrangement is the one in which there are five vertical rows, but, in order to reach a leaf standing directly over the one started from, a spiral is traced twice around the stem. The angular divergence between two successive leaves, therefore, is two fifths of the circumference or 144°, and this arrangement is designated by the fraction |. It has been found that any fraction may be derived by adding the numerators and denominators of the two preceding fractions. For example, the next higher arrangement would be f, which means that the angular divergence is three eighths the circumference of the stem, that is, eight leaves are passed before one is reached standing directly over the one started from, and in finding the eighth leaf a spiral has been traced three times around the stem. Such high orders of arrangement, as 5-13, 8-21 etc. are displayed in pine cones.
Phyllox'era. See GRAPE-PHYLLOXERA.
Phys'ical Ed'ucation in some schools and colleges includes the physical examination of pupils and students; their personal guidance in matters relating to health; the class instruction given in hygiene; and the teaching and supervision of muscular exercise involved in gymnastics and athletics. Physical education refers more technically to the employment of large forms of muscular movement in the education of the young for the development of organic power and efficiency and for the attainment of mental and moral qualities which depend upon muscular activities and habits. As modern life becomes more sedentary and specialized, particularly for those who live in cities, the importance of physical education increases. As the scope of modern education broadens and as educational methods become more adequate in preparing pupils for practical living, the need of physical education is more clearly recognized. This term refers in theory to the plan and benefits of muscular or motor activities in general in the education of the young and is concerned with the physiology and psychology of muscular exercise where-ever it occurs. Practically, however, physical education is directly responsible for the fundamental movments of the body not required otherwise nor sufficiently by the school or by life outside of school.
In the development of modern education it is domestic science, manual training and school excursions that have to some extent supplied the need for large neuromuscular movements; but these are by no means sufficient for all the needs of the developing child, and they are not intended or adapted primarily for general organic training. Under more primitive conditions of life in the past grown people and children maintained health and became strong, courageous and self-reliant by varied work and
