FLOWER 



FLOWER 



1247 



are united higher up into groups of two and three, as 

 in many mints, the upper more or less erect, the lower 

 spreading, the corolla is hilahiale (Fig. 1526). A partic- 

 ular type of irregular polypetalous corolla is the so- 

 called papilionaceous corolla (Fig. 1527) found in the pea 



1522. Stamens 

 of erica (left) and 

 vaccixuum. 



1523. A salver-shaped coroUa. 



family and consisting of a standard, two lateral wings, 

 and a keel. A regular corolla is radially symmetrical, 

 possessing an iniinite number of planes of symmetry 

 (actinomorphic) , while most irregular flowers possess 

 but one plane of symmetry {zygomorphic) . A few pos- 

 sess no such plane (as Carma). Gamopetalous corollas 

 fall into certain types based on the shape of the tube 

 and limb. The more common types are rotate, salver- 

 form, funnelfortn, bell-shaped, tubular, anfl urceolate. 



The corolla may be vari- 

 ously colored. White flow- 

 ers owe their color to light 

 reflected from air which is 

 between the cells of the 

 petals, as shown by the 

 fact that when waterlogged 

 these petals become trans- 

 parent. Yellows and oranges 

 are usually due to abun- 

 dant minute color bodies 

 (chromoplasts) located 

 within the cells of the petal. 

 Reds and blues are due to 

 colored cell-sap. 



Calyx. — Surrounding the 

 corolla is another set or 

 whorl of organs, the calyx, 

 the individual organs of 

 which are sepals. The calyx is usually composed of as 

 many sepals as there are petals, but in the Portulacaceae 

 there are but two sepals, while in some plants there are 

 many. In many of the Ranunculacea; and other fami- 

 lies they are colored like petals and replace these organs. 

 In the Easter hly and tuUp they are similar to the 

 petals. In the Compositse the calyx is reduced to 

 scales or bristles or is absent entirely. The sepals are 

 frequently connate (gamosepalous), and the resulting 

 structure is often irregular. The calyx and corolla are 

 together termed the floral envelopes. If they are simi- 

 lar in appearance, and, therefore, difficult to recognize, 

 as in the Easter hly, they are collectively termed 

 perianth. 



Disk (Figs. 1528, 1529).— In many 

 plants a glandular disk, or series of 

 glands corresponding to such a disk, 

 is foimd. When present, this disk 

 may lie either between the stamens 

 and pistil (intrastajninal) as is the 

 common case, or more rarely be- 

 tween the stamens and petals 

 (extrastaminal) . The genus Acer is 



1524. Funnelform corolla of 

 morning-glory. 



pecuhar in having some species with an intrastaminal 

 disk while in others it is extrastaminal. By some 

 morphologists this disk is considered a fifth set of organs 

 in the flower, while by others it is considered merely as 

 an outgrowth of the floral axis or receptacle on which 

 all other parts of the flower are in- 

 serted. The disk is in many cases 

 characteristic of whole families, which 

 led Bentham and Hooker to place 

 these f;imilies together in the series 

 Disciflorse. The di.sk also occurs in 

 other families not obviously related. 

 It forms a ring about the styles in 

 some Rubiaceae. The glandular cup of 

 Populus and the finger-like gland of 

 Salix are probably to be referred here, 

 although by some they have been 

 interpreted as a reduced perianth. The 

 disk usually functions as a nectary. In 

 shape and structure it is very diverse. 

 It may be cup-shaped, saucer-shaped, annular, regular, 

 or irregular; or it may be of separate glands, either 

 simple or variously lobed. It may fine the cup of the 

 perigynous flower or it may be adnate to the surface 

 of the ovary. 



Receptacle (Figs. 1530, 1531).— The apex of the 

 stem on which the various floral organs are inserted is 

 termed the receptacle or torus. This is normally a 

 simple club-shaped thickening of the summit of the 

 stem. In the strawberry it is much enlarged and fleshy, 



1526. Labiate 

 corolla of salvia. 



1527. A papilionaceous 

 corolla. — The sweet pea. s, 

 standard; w, w, wings; k^ 

 keel. 



1528. Showing the disk in the 

 willow flower. Pistillate flower 

 at a; staminate flower at b. 



1525. Rotate co- 

 rolla and connivent 

 stamens of solanmn. 



forming the greater part of the fruit. In the raspberry it 

 remains on the plant when the "fruit" is removed. In 

 the Compositai there is a common receptacle for all 

 the flowers of the head, as well as for each individual 

 flower. In the caper family the receptacle is often pro- 

 longed upward, forming a stalk for the ovary within 

 the flower (gynophore). 



In the Rosaceae, Onagracese, Saxifragacese, and in 

 various other plants, the stamens, petals and sepals 

 are perigynous, that is they are inserted on the edge of a 

 cup-shaped organ which springs either from below the 

 ovary or from its summit. The view has been held 

 that the gamosepalous calyx here bears the stamens 

 and petals on its tube. Another early proposed view 

 has in recent years gained ground rapidly and is now 

 widely accepted. This view interprets 

 the cup as a hollowed receptacle 

 hkened to a glove-finger when the apex 

 is slightly pushed in. 

 The ovary at the 

 bottom of the cup is 

 really apical as usual, 

 while the sepals, 

 petals and stamens, 



located at the higher 1529. Dig^s in flowers of 



margin of the cup, maple family. 



