CONVOLVULACEAE

convolvulaceae, a botanical natural order belonging to the series tubiflorae of the sympetalous group of dicotyledons. it contains about 40 genera with more than 1000 species, and is found in all parts of the world except the coldest, but is especially well developed in tropical asia and tropical america. the most characteristic members of the order are twining plants with generally smooth heart-shaped leaves and large showy white or purple flowers, as, for instance, the greater bindweed of english hedges, _calystegia sepium_, and many species of the genus _ipomaea_, the largest of the order, including the "convolvulus major" of gardens, and morning glory. the creeping or trailing type is a common one, as in the english bindweed (_convolvulus arvensis_), which has also a tendency to climb, and _calystegia soldanella_, the sea-bindweed, the long creeping stem of which forms a sand-binder on english seashores; a widespread and efficient tropical sand-binder is _ipomaea pes-caprae_. one of the commonest tropical weeds, _evolvulus alsinoides_, has slender, long-trailing stems with small leaves and flowers. in hot dry districts such as arabia and north-east tropical africa, genera have been developed with a low, much-branched, dense, shrubby habit, with small hairy leaves and very small flowers. an exceptional type in the order is represented by _humbertia_, a native of madagascar, which forms a large tree. the dodder (q.v.) is a genus (_cuscuta_) of leafless parasites with slender thread-like twining stems. the flowers stand singly in the leaf-axils or form few or many flowered cymose inflorescences; the flowers are sometimes crowded into small heads. the bracts are usually scale-like, but sometimes foliaceous, as for instance in _calystegia_, where they are large and envelop the calyx. the parts of the flower are in fives in calyx, corolla and stamens, followed by two carpels which unite to form a superior ovary. the sepals, which are generally free, show much variation in size, shape and covering, and afford valuable characters for the distinction of genera or sub-genera. the corolla is generally funnel-shaped, more rarely bell-shaped or tubular; the outer face is often marked out in longitudinal areas, five well-defined areas tapering from base to apex, and marked with longitudinal striae corresponding to the middle of the petals, and alternating with five non-striated weaker triangular areas; in the bud the latter are folded inwards, the stronger areas being exposed and showing a twist to the right. the slender filaments of the stamens vary widely, often in the same flower; the anthers are linear to ovate in shape, attached at the back to the filament, and open lengthwise. some importance attaches to the form of the pollen grains; the two principal forms are ellipsoidal with longitudinal bands forming the _convolvulus_-type, and a spherical form with a spiny surface known as the _ipomaea_-type. the ovary is generally two-chambered, with two inverted ovules standing side by side at the inner angle of each chamber. the style is simple or branched, and the stigma is linear, capitate or globose in form; these variations afford means for distinguishing the different genera. the fruit is usually a capsule opening by valves; the seeds, where four are developed, are each shaped like the quadrant of a sphere; the seed-coat is smooth, or sometimes warty or hairy; the embryo is large with generally broad, folded, notched or bilobed cotyledons surrounded by a horny endosperm. _cuscuta_ has a thread-like, spirally twisted embryo with no trace of cotyledons. [illustration: _convolvulus sepium_, slightly reduced. 1. flower cut vertically. 2. fruit, slightly reduced. 3. seed cut lengthwise showing embryo. 4. embryo taken out of seed. 5. horizontal plan of arrangement of flower.] the large showy flowers are visited by insects for the honey which is secreted by a ring-like disk below the ovary; large-flowered species of _ipomaea_ with narrow tubes are adapted for the visits of honey-seeking birds. the largest genus, _ipomaea_, has about 400 species distributed throughout the warmer parts of the earth. _convolvulus_ has about 150 to 200 species, mainly in temperate climates; the genus is principally developed in the mediterranean area and western asia. _cuscuta_ contains nearly 100 species in the warmer and temperate regions; two are native in britain. the tubers of _ipomaea batatas_ are rich in starch and sugar, and, as the "sweet potato," form one of the most widely distributed foods in the warmer parts of the earth. several members of the order are used medicinally for the strong purging properties of the milky juice (latex) which they contain; scammony is the dried latex from the underground stem of _convolvulus scammonia_, a native of the levant, while jalap is the product of the tubercles of _exogonium purga_, a native of mexico. species of _ipomaea_ (morning glory), _convolvulus_ and _calystegia_ are cultivated as ornamental plants. _convolvulus arvensis_ (bindweed) is a pest in fields and gardens on account of its wide-spreading underground stem, and many of the dodders (_cuscuta_) cause damage to crops. convoy (through the fr. from late lat. _conviare_, to go along with, from lat. _cum_, with, and _via_, way; "convey" has the same ultimate origin [see conveyance], neither word being connected, as has sometimes been supposed, with lat. _convehere_, to carry together), a verb and noun now almost exclusively used in military and naval parlance. as a verb it signifies in the first instance to accompany or to escort; and in the 17th century we even hear of cavalry "convoying" infantry, but its meaning was soon complicated by the growing use of the word "convey" in the sense of "to carry," and as the usual task of an escort was that of accompanying and protecting vehicles containing supplies, the noun "convoy" (fr. _convoi_) was introduced and has thenceforward in land warfare meant a train of vehicles containing stores for the use of troops and its guard or escort. sometimes even the word is found in the meaning of the train of vehicles without implying that there is an escort, so far has the original meaning become obscured; but the idea of military protection is always present, whether this protection is given by a separate escort or provided by the weapons of the drivers themselves. in naval warfare the term is used to describe a method adopted for defending merchant ships against capture. it was usually applied to the vessels to be protected--as for example "the baltic convoy," or "captain montray's convoy." until the 17th century the english term was "to waft" and the warship employed to guard the traders on their way was called "a wafter." the practice of sailing in convoy for mutual protection was common in the middle ages, when all ships were more or less armed and the war vessel was not entirely differentiated from the trader. thus the ships of the great german confederation of cities known as the hanseatic league were required to sail in convoy. so were the six trading squadrons which sailed yearly from venice. the masters of all the vessels were required to obey the authority of an officer who had the general command. in the 16th century the spanish trade with america was compelled by law to sail in convoys (_flotas_), in order to avoid the danger of capture by pirates to which single ships were exposed. in the 17th and 18th centuries the use of convoy was universal. dutch, french or british ships were collected at a rendezvous, and were accompanied by warships till they reached the point at which they were compelled to separate in order to go to their various destinations. the main danger was near the enemy's ports. an example of the way the duty was discharged may be found in the newfoundland convoy. they sailed from england under the direction of a naval officer and the protection of his ships, commonly a forty- or fifty-gun ship with a smaller vessel in attendance. the convoy sailed to the banks of newfoundland. when they had filled up with stock fish, they were escorted across the atlantic by the same officer. he accompanied those of them bound to the mediterranean to the port of leghorn, and, when they had unloaded and reloaded, saw them home. all cases were not so simple. the ships engaged in the east and west india trade, for instance, sailed together. in the channel they were protected by the main strength of the fleet. when beyond the scilly islands they were left to the care of a smaller force, and continued together till in the neighbourhood of madeira, when they separated. convoys were subject to attack in two forms, by strong squadrons which overpowered the guard, and by privateers, corsairs and isolated cruisers. this latter peril was much increased in the case of british commerce by the reluctance of the merchant captains to obey the naval officers. they were very much inclined to separate from the convoy as they approached their destination in the hope of forestalling rivals. as a natural consequence they were frequently captured by hostile privateers. french naval officers had authority and large powers of punishment over merchant skippers. the british naval officers had not. in 1803-34, on the renewal of the war with france, the british government saw the necessity for regulating convoy more strictly than had hitherto been the case. it therefore passed "an act for the better protection of the trade of the united kingdom during the present hostilities with france." by this act (the 43rd geo. iii. cap. 57) all vessels not exempted by special licence were required to sail in convoy and to conform to strict regulations, under penalties of £1000 (or, when the goods included government stores, of £1500) and the loss of all claim to insurance in case of capture. (d. h.) the object of convoying is to attach an official public character to the convoyed ships, i.e. a sort of assimilation of them to the escorting ship or ships of war. thus european states and jurists hold that the declaration of the commander of the convoy, that there is no contraband of war on board the convoyed ships, pledges the national good faith, and must be assumed to be correct in the same way as it is assumed that the convoy itself is carrying no contraband of war. great britain has never taken this view. down to 1907 she had maintained that it is materially impossible for any neutral state to exercise the necessary supervision to secure absolute accuracy of the ship's papers. number 29, however, of the instructions given by the government to the british plenipotentiaries at the hague conference of 1907 stated that "h.m. government would ... be glad to see the right of search limited in every practicable way, e.g. by the adoption of a system of consular certificates declaring the absence of contraband from the cargo...." as the greater includes the smaller, we may assume that, if a consular certificate might suffice to exempt from the exercise of search, the state guarantee of a convoy would certainly suffice. the london convention on the laws and customs of naval war has laid down the rules as to convoys in the following terms: neutral vessels under national convoy are exempt from search. the commander of a convoy gives, in writing, at the request of the commander of a belligerent warship, all information as to the character of the vessels and their cargoes, which could be obtained by search.--art. 61. if the commander of the belligerent warship has reason to suspect that the confidence of the commander of the convoy has been abused, he communicates his suspicions to him. in such a case it is for the commander of the convoy alone to investigate the matter. he must record the result of such investigation in a report, of which a copy is handed to the officer of the warship. if, in the opinion of the commander of the convoy, the facts shown in the report justify the capture of one or more vessels, the protection of the convoy must be withdrawn from such vessels.--art. 62. (t. ba.)