Page:The American Cyclopædia (1879) Volume X.djvu/273

 LEAF LEAKE 267 the wound which would otherwise he left is covered with a prolongation of the epidermis of the stem. The leaf scars in the horse chestnut and ailantus are large, and show the points from which issued the bundles of woody fibre to form the framework of the leaf. In palms and some other monocotyledonous plants the leaves do not fall, but wither and decay upon the tree. The study of the morphology of the leaf presents an endless variety to a close observer, and nothing in relation to the subject is more interesting than the many ab- normal forms in which leaves, besides per- forming their proper offices as foliage, are made to serve the plants in other respects, or are quite turned aside from their normal uses to those which ordinarily belong to the root or stem. The scales which make up the greater part of a lily bulb are only the bases of former leaves which have become thick and fleshy by the accumulation of nutriment which is to be used in the future growth of the plant. This conversion of leaves into storehouses of food is strikingly shown in some seeds, in many of which the first leaves of the embryo plant, the cotyledons, or seed leaves as they are popularly called, are quite distorted by the accumulation of starchy and other matters intended to nour- ish the young plant; the common bean is a familiar illustration of this; in the bean the seed leaves fall away after they have parted with their store, but in the squash and others of its family the seed leaves, after they have served their purpose of helping the growth of the young plant, increase in size, turn green, and become proper leaves. The seed leaves of the oak, pea, and others are so distorted by the food they contain that they never come to the light and appear as proper leaves. The scales which surround the buds of deciduous trees are only modified leaves, some trees showing a regular gradation from the brown dry scale to the fully developed green leaf. In the barberry the leaves often appear as spines, and in Fouquieria, one of the chaparral plants of western Texas, the stem of Tvhich is formidably covered with sharp points, the spine is the midrib of the leaf from which the blade has fallen away. The common pea affords an illustration of the conversion of a portion of the leaf into a tendril to aid the plant in climb- ing, and in a plant of the same family (lathy- rus aphaca) the whole leaf is developed as a tendril. Among the abnormal forms of leaves, none are more interesting than the ascidia or pitchers, in which, as in our native pitcher plants (Sarracenia), the whole leaf forms a pitcher, or, as in nepenthes, the pitcher is an appendage to the leaf. (See PITCHER PLANTS.) Still more wonderful is the adaptation of the leaf to serve as a trap to catch insects, as in our carnivorous Venus's fly-trap. (See Dio- N.EA.) In this brief description of the leaf it has been considered in only its normal condi- tion of foliage and some of its readily under- stood transformations, but the botanist regards the flower and its resulting fruit of whatever kind as only peculiar modifications of the leaf. The idea of tracing all the floral organs to one type, the leaf, had been hinted at before Linnseus, and the great botanist himself did not present the matter in such a way as to attract much attention ; the poet Goethe pro- posed the theory in much the same form as it is now held, but it was not until the elder De Can- dolle presented it that the theory of metamor- phosis was generally accepted. The arrange- ment of the leaves upon the stem is such as to give the greatest possible amount of divergence, and though they may appear to be scattered without order, they are arranged in a manner definite for such species, and this has given rise to a distinct department of botany involving mathematical principles, called phyllotaxy. It has already been hinted that the chief function of the leaf is to bring the interior of the plant into communication with the sun and air ; it receives the liquid taken up by the roots, and in its tissues evaporation goes on ; it not only permits but regulates evaporation by the won- derful mechanism of the leaf pores. But evap- oration is by no means the sole office of the leaf ; the air with its gases has free access to its inte- rior, and here takes place the process of assimi- lation, about which so little is known, in which carbon, oxygen, hydrogen, and nitrogen are converted into organic compounds. We know that the chlorophyl is an active agent in effect- ing these changes, and that sunlight is essential to the proper performance of the leaf's func- tions. As water is so largely evaporated in the leaf, and as this, coming from the soil, must contain more or less inorganic matter in solu- tion, it is not surprising to find that the leaf contains a large amount of earthy matter or ash, and that leaves in autumn have a larger percentage of ash than vernal leaves; the leaves show upon analysis 10 to 30 times as much ash as the wood of the same tree. LEAGUE (Sp. legua ; Fr. lieue), a measure of length used for estimating distances at sea, and by European nations upon land also. The nautical league is 2 J o of a degree, or 3 equatorial miles, or 3'457875 statute miles. The land league in England is 8 statute miles. In France it has been used for different distances, as the legal post league, 2*42 English miles, and the league of 25 to the degree, or 2 -77 English miles. The Spanish league is still more varia- ble, sometimes 17 and again I7i being reckoned to the geographical degree. Upon the modern roads 8,000 Spanish varas, or 7,418 English yards, are estimated one league. The term is supposed by some to have come from the Celtic leach, a stone ; and by others the Gallic leuca, league, is traced to the Greek /lew<5f, white, white stones being used by the Gauls to mark distances upon the roads. LEAKE, a central county of Mississippi, trav- ersed by Pearl river ; area, 576 sq. m. ; pop. in 1870, 8,496, of whom 3,005 were colored. It has a rolling surface and a light sandy soil.