394 



COMPOSITE 



COMPOSITION 



In shortening down, or less figuratively, in arrest- 

 ing the inflorescence into a head, the bract of each 

 separate flower remains in place ; and in a Zinnia, 

 or sunflower, we find each floret with its separate 

 bract throughout the whole capitulum ; in most 

 cases, however, these disappear. Those of the 

 outermost florets, however, together with the im- 

 mediately lower leaves of the flower-axis (which 

 bear no florets, and are thus in strictness not 

 entitled to their common name of bracts) become 

 usually crowded into an involucre. This subserves 

 in bud the protective purposes of a calyx to the 

 whole inflorescence at once, and thus the calyx of 

 the separate florets becomes unnecessary. In its 

 place we find at most a circle of fine downy 

 hairs, which may be characteristically serrated or 

 feathered, and which only reach full development 

 and usefulness when the fruit has to be distributed. 

 On account of its merely epidermic nature and late 

 appearance, its calycirie nature has been denied, 

 .and the term pappus substituted ; the evolutionist 

 need, however, feel little hesitation in regarding 

 the pappus as simply representing the epidermic 

 fringe of a reduced calyx, nor is verificatory evidence 

 wanting. The stamens grow upon the united corolla 

 .and themselves unite by the anthers, thus forming a 

 ring or rather pollen-bearing tube, up through which 

 the style grows, all much as in bells. The style 

 bears two stigmas, indicating an originally two- 

 carpelled arrangement, but the ovary is one-celled, 

 .and contains only a single ascending ovule. The 

 ovary hardens as a nutlet, which is commonly 

 floated away upon the wind when ripe by help of 

 its pappus ; it may be anchored where it descends 

 by its minute grappling-hooks or serrations. In 

 this way it is conveyed to new soil, it may be at 

 a great distance, an obvious advantage, alike to 

 the species or the individual, when germination 

 takes place. 



The classification of so many closely related 

 genera and species into larger groups is one of the 

 most difficult problems of the systematist, and all 

 attempts must as yet be admitted to be largely 

 artificial. The method of Jussieu is to separate 

 ( 1 ) those in which the florets are all tubular, as in 

 the thistles ( even though the outer be enlarged as 

 in corn-flowers see CENTAURY ), as Cynarocephalae ; 

 (2) those in which, while the inner florets are 

 tubular, the outer are ligulate as in daisy, sun- 

 flower, &c., as Corymbifera;, and (3) those in which 

 all the florets are ligulate, as in dandelion or 

 chicory, as Cichoracese. The more recent method 

 of De Candolle is now more generally adopted : his 

 distinctions are ( 1 ) Tubuliflone, including those 

 which have mainly tubular florets, although the 

 ray be ligulate, thus abandoning the attempt to 

 separate the first two divisions of Jussieu; (2) 

 Liguliflorse, with florets all ligulate, corresponding 

 to Cichoracese ; (3) Labiatiflorse, with florets all 

 bi -labiate, a small South American group. But 

 while this last group has unquestionable distinct- 

 ness, the value of both preceding classifications in 

 -other respects is shown to be somewhat superficial 

 by the familiar faot that in cultivation tubular 

 florets tend to become ligulate (in inaccurate 

 popular phrase, double}. Thus we see the wild 

 daisy, dahlia, chrysanthemum, &c., alike practi- 

 cally passing into the ligulate group on cultiva- 

 tion. 



Although many composites are cultivated and 

 useful plants, none attain the highest economic 

 importance : yet the artichoke, and Jerusalem 

 artichoke, salsafy, lettuce, endive, &c., are 

 familiar inmates of the kitchen -garden, while 

 chicory is extensively cultivated as a substitute 

 for coffee, and even sometimes, as well as Jerusalem 

 .artichoke, for the purpose of feeding domestic 

 animals. A very few, like safflower and saw-wort, 



yield dyestuffs ; from the seed of others e.g. sun- 

 flower, a bland oil is expressed, while many are of 

 time-honoured repute for their medicinal properties 

 e.g. chamomile, arnica, wormwood, elacampane, 

 &c. A still greater number e.g. headed by 

 dahlias and sunflowers, asters and chrysanthemums 

 are esteemed ornaments of our flower-gardens, 

 particularly in the latter part of summer and in 

 autumn. Being mostly herbs, or rarely shrubs, 

 the order is quite unimportant as regards timber ; 

 the Siriehout ( Tarchonanthus camphoratus), a small 

 tree of the Cape of Good Hope, is, however, close- 

 grained and beautiful. 



For detailed information, see systematic works 

 such as Luerssen, Med. Pharm. Botanik ; Baillon, 

 Histoire des Plantes ; or Engler's Pflanzen-familien, 



Composite Order. See COLUMN. 



Composition. Under the title Composition 

 and Resolution of Velocity and Forces, we deal 

 with one of the fundamental problems in mechanics 

 viz. to compound two velocities (or forces) into 

 a single velocity (or force) which shall be their 

 equivalent. We shall consider it as applied to 

 velocities in the first place. 



If a point is moving with two independent velo- 

 cities in any direction, it moves in some one definite 

 direction with a definite speed. This single velocity 

 ( for the term includes the idea of direction as well 

 as speed ) is equivalent to the two component velo- 

 cities, and is termed their resultant. A good 

 example is afforded by a ball thrown up in a 

 moving railway carriage ; it partakes of the train's 

 motion horizontally, while it also simultaneously 

 moves vertically upwards. 



When the two components are in the same 

 straight line, their resultant is in all cases equal 

 to their algebraic sum. In the case of velocities 

 in different directions, the magnitude and direction 

 of their resultant is obtained by the following 

 theorem, known as the Parallelogram, of Velocities: 

 If a point A move with two velocities, represented 

 in magnitude and direction by AP and AQ respec- 

 tively, their, resultant will be similarly represented 

 by AR, the diagonal of the parallelogram of which 

 AP and AQ are 

 conterminous sides. 

 For, let the point 

 move along AQ with 

 velocity AQ, and let 

 the page be in motion 

 in the direction AP 

 with velocity AP. 

 After a unit of time 

 has elapsed, the point will have moved from A to 

 Q along AQ, but, owing to the motion of the page, 

 the line AQ will have moved into the position PR, 

 so that the point will really be at R ; hence its 

 motion has been in the direction AR, with a velo- 

 city whose magnitude is represented by AR. 



Similarly, we may compound any number of 

 velocities in one plane into a single resultant. In 

 the case where three components are not coplanar, 

 a corresponding theorem, the Parallelepiped of 

 Velocities, is used to find the resultant. 



The resolution of velocities is exactly the con- 

 verse problem ; for where a directed length such as 

 AR can be made the diagonal of a parallelogram, 

 then the conterminous sides are the components. 

 Of course, in this manner, an infinite number of 

 pairs of components can be obtained, each having 

 the given velocity as their resultant. But the 

 resolutions usually required are those in which the 

 components are at right angles. 



Since forces can be graphically represented in the 

 same manner as velocities, all that has been said 

 of velocities applies equally well to forces ; and 

 obvious changes in the terminology at once give 



