FLOWER 



FLOWER 



593 



leaves are formed, the intervening parts grow very lit- 

 tle, and so do not separate the successive leaves or cir- 

 cles of leaves. The torus is more or less broadened or 

 elongated to permit the suitable growth of the crowded 



Torus and fruit of 

 Raspberry. 



leaves. In the strawberry it is high, dome-shaped 

 (Figs. 826, 827) ; in the raspberry the torus remains 

 (S, Fig. 828) when the little drupes are removed; in the 

 rose it is urn-shaped, bearing the leaves on the edge and 

 inner face ; in the mouse-tail it is much elongated. 

 When a number of flowers are crowded together their 

 leaves are developed from a common torus, as in sun- 

 flower and chrysanthemum and other members of the 

 Compositae (Fig. 829). The common torus may be 

 broad and flat, with the flowers scattered over it, as in 

 Dorstenia (Fig. 732) ; or even hollow, as in the fig (Fig. 

 821), with the minute flowers on the nearly enclosed 

 inner face. 



Floral leaves. The leaves of the flower form two 

 series ; the outer protective and attractive leaves, the 

 floral leaves, and the inner sporangial leaves. The floral 

 leaves are usually distinguishable into an outer set, the 

 calyx, and an inner set, the corolla. The calyx leaves, 

 when separate, are called sepals, and the corolla leaves 

 petals. The sepals are more or less different from the 

 petals in size, shape and color. They are oftenest green, 

 and usually smaller and simpler than the petals. In the 

 bud they usually completely cover the inner leaves. 

 The sepals and petals oftentimes do not remain distinct 

 throughout their development, but each set grows as a 

 single piece; a fact which has been made the basis of 

 classification of the angiosperms. Corollas of a single 

 piece are said to be gamopetalous (Fig. 830). The sepals 

 are more commonly inseparate than the petals. 



The apparent union of the floral leaves comes about 

 generally in this way: On the young torus the rudi- 

 ments of the sepals and petals arise as rounded knobs, 

 which for a longer or shorter time grow independently. 



829. Section of a compositous head. 

 Showing the common torus at e. 



If they develop independently until their growth ceases, 

 the sepals or petals are distinct, each one being sepa- 

 rately attached to the torus. On the other hand, after the 

 leaf rudiments have grown independently for a time, a 

 zone of the torus, both under and between two or more 

 adjacent rudiments, may begin to grow, lifting them on 



its margin. In that case, when fully grown the calyx or 

 corolla appears as a single piece, whose free edge is 

 more or less deeply lobed, according to the relative dura- 

 tion of independent development of the rudiments. 



The calyx and corolla are sometimes united. This 

 comes about in a similar way. Each begins to develop 

 independently ; later the tissue between calyx and co- 

 rolla shares in the growth and both are raised on a com- 

 mon base. 



The form of the mature floral leaves depends largely 

 on the relations of the flower to insects, which visit the 

 flowers for nectar or pollen. The floral leaves are often 

 irregular and unequal, so as to form suitable landing 

 places, nectar glands, guides to the nectar, etc., all de- 

 vices to facilitate the proper transfer of pollen by the 

 visitors; e. g., the sweet pea and other papilionaceous 

 flowers, most orchids, etc. (see Pollination). 



The color of the corolla and adjacent parts is due to 

 the presence in the cells of colored sap or special color- 

 bodies. In the latter case the pigment is sometimes 

 crystalline. It is not possible to determine without mi- 

 croscopic examination in which way the color is pro- 



830. A gamopetalous corolla of Eggplant. 



duced. Most blues are due to colored sap; many yel- 

 lows and reds to color-bodies. 



The velvety appearance of many petals is produced by 

 the outgrowth of the surface cells into conical or dome- 

 shaped protuberances. 



The odor of flowers is usually due to the presence of 

 volatile oils in the surface cells of the petals or sepals, 

 or both. These oils are present in small amount only. 

 They are sometimes found only on the outer face, or 

 only on the inner face, or they may even be restricted 

 to certain lines or patches. 



The stamens . The stamens commonly consist of two 

 parts, a stalk, the filament, bearing a larger portion, the 

 anther (Fig. 831 ) . The filament is usu- 

 ally rigid enough to sustain the weight 

 of the anther, but at maturity it is 

 sometimes so long and slender that the 

 anthers hang as by a thread (so in 

 grasses). The filament is sometimes 

 so short as to seem wanting; the anther 

 is then said to be sessile. The fila- 

 ments are often united with one 

 another or with the corolla by the 

 mode of growth already described. In 

 the latter case the stamens seem to 

 arise from the corolla. Only rarely 

 are the stamens and carpels united. 



The anther is the part of the stamen 

 which bears the spore-cases or pollen 

 sacs (sporangia). (The sporangia are 

 not always borne on stamens. In a few 

 plants they are sunk in the stem of the 

 flower.) Of these there are commonly flower of Willow, 

 four, more rarely two or one. When Showing two sta 

 the anther was looked upon as a cham- 

 bered body, the sporangia were called 

 thecae, or cells. Thus in descriptive botany the anther 

 is said to be w 2-celled" or 4-celled." The sporangia are 

 partly free and partly imbedded in a mass of tissue 



831. Staminate 



their an- 

 thers are at a. 



