Page:The New International Encyclopædia 1st ed. v. 20.djvu/815

* XEBOPHYTES. G93 XIMANA. may partially inhibit the natural processes of absorption and conduction of water by plants. The more prominent xerophytic structures may be defined as follows; First, reduction in sur- face as coin])ared with plants of other areas. This reduction may be permanent, as in the case of cacti and desert shrubs, or where leaves are entirely absent, reduced to very small dimen- sions; or temporary, as illustrated by plants which slied their leaves at the beHinninf,' of a season, dry because of heat, as in deserts, or cold, as in high latitudes and altitudes. Second, vertical placement of the foliage organs, illus- trated not only by the cacti, in which the chloro- phyll worlc is done in the stems, but also by the so-called compass plants, where the leaves assume a profile or vertical position instead of the hori- zontal. Third, the annual habit is typified by a sliort life cycle restricted to the rainy season. Fourth, bulb and tuber plants, in which the vegetative development is conspicuous during the rainy season, but ceases during the dry pe- riod. Fifth, ligneous tissue. In many xero- pliytic areas a very high proportion of the plants are trees or shrubs. Sixth, storage organs, as in succulent plants such as cacti, various sedums, and aloes. Seventh, modifications of tissue; for example, hairs as in some alpine plants, such as edelweiss; thick-walled epidermis due to cutinization; wa.xy deposits, varnish or mineral crusts on the epidermis; cork in woody plants; abundant palisade cells; reduction of air spaces, occurrence of stomata mainly or wholly on the lower surface, away from the light ; below the surface, as in the carnation: and protection of stomata by hairs, as in the oleander. It will be seen that most structures can be re- garded as advantageous, since they protect jdants against excessive transpiration. For example, if the cork and cutin layers, which are relativcl.v impermeable to water, be removed, the loss of water is tremendousl.v accelerated. Some of these structures can be shown lv experiment to be the direct result of xeropbytic conditions, although in most cases the exact stimulating cause is not clear. Doubtless the most potent factor is a dry atmosphere. Experiments show that dvv air as compared with moist air accelerates the develop- ment of cutin. cork, coUenchvma, bast, waxy tis- sue, incrustations, and lignin. These structures may be produced experimentally in mesophvtes grown under xerophytic conditions. It seems, therefore, that many plants have a high degree of plasticity, enabling them to ada])t themselves in case of need to xerophytic conditions. It must be remembered, however, that such adaptation must be in harmony with physical and chemical laws, and that the plants can in no way overstep the bounds prescribed for them. It is quite likely that the structures whose development has been found to be accelerated in xerophytic conditions ■ are in reality caused mechanically by excessive transpiration, and a consequent deposition of sub- stances such as cutin, suberin. lignin, etc., which might otherwise have been held in solution. This deposition, which is thus due to a mechanical cause, is. however, of direct advantage to the plant. jSIesophvtes which are transferred to xerophytic conditions a^iproach normal xero- ph.vtes in the reduction of leaf and stem surfaces. This reduction, while of advantage to the plant, may also doubtless be referred to mechanical or climatic causes. For example, the available food materials may be less abundant in the xero- phytic soil, the absorption may be less, and transpiration may be great. All of these con- ditions would probably tend to cause reduction. See Leaf. The .xerophytic formations of the world may be sul)divided into two great classes: climatic, oc- curring over wide areas, and edaphic, occurring over limited areas. For examples of the former, see Alpine Plant; Arctic Reoion; Desert Vegetation; Tundba; Fore.st; (Jbasslaniks; Pkairie. For examples of the latter, see Beach Plants ; Dune Vegetation ; Heath ; Rock Plants; Swamp. XERXES, zerk'sez (Lat., from Gk. S^^'fT/t, from OPer. XsayurM, mighty hero). Three kings of Persia, the first two of whom belonged to the celebrated Acha>menian dynasty. — Xerxes I. (C..519-C.4G5 B.C.), commonly identified with the Ahasuerus of the Bible, was the son of Darius I. Hystaspis and of Atossa, daughter of Cyrus. Born after the accession of his father, in B.C. 521, Xerxes seized that pretext to supersede three older brothers, and ascended the throne upon the death of Darius in 485. His first act was to subdue the revolt of Egypt. He then spent three years in preparing to punish the Greeks for the humiliations the,v had put upon his' father. Col- lecting at Critalla, in Cappadocia, an army which has been estimated to number a million, he marched to Sardis (Lydia) and thence set out for the Hellespont in the spring of 480. A fleet of 1200 sail bad in the meantime assembled at Doriscus, in Thrace. The fate of this unwieldy expedition, successful first at Thermopyhr. but crushed at Salamis (480) and at PlatTca (479), is one of the most familiar stories in history. ( See Greece. ) Xerxes, who had fled from Cireece after the disaster to his fleet at Salamis. ad- vanced against Babylon, where Samaserba the Chaldaean had usurped the royal power. After razing the temples of the city he returned to Persepolis and Susa. He was murdered with his eldest son, Darius, by Artabanus, captain of the guard.^XERXES II. (c.450-c.425 B.C.) was the son of Artaxerxes I. and Damaspia, and the grandson of Xerxes I. He ascended the throne upon the murder of his parents (e.425). After a reign of fort.v-five days he was himself assas- sinated and was succeeded by his half brother Sogdianus or See.ydianus. — Xerxes III. was the name given to Oarses, who reigned in B.C. 337- 336. He was controlled by the eimuch Bagoas, by whom he was proclaimed. XICAQUE, iie-ka'ka. An important Central American trilie. constituting a distinct linguistic stock, occupying the region of the upper Ulua or Sulaco River, in Yoro and Santji Barbara dis- tricts. Northern Honduras. They are said to have a compact tribal organization under a head chief, who is elected for life. They number about GOOO. XIMANA, ne-mii'na. A wild tribe in the forests between the Putuma.vo and Yapura rivers, northern aflluents of the Amazon, in Western Brazil. Although said to be industrious, they are entirelv savage in their mode of life. They kill their first-born children, and burn the bones of their dead, mingling the ashes with their drink.