1246 



FLOWER 



FLOWER 



Ovaries are sometimes raised on a stalk within the 

 flower, as in the caper family (gynophore) and in Coptis 

 (thecophore) . The styles and stigmas are frequently much 

 modified for pollination purposes, as in the orchids and 

 in the pitcher plant (Sarracenia) . 

 The andrcecium (Figs. 1520- 

 1522). Surrounding the pistils 

 are found one or more whorls of 

 organs called stamens, collec- 

 tively termed the andrcecium 

 (male household). A stamen 

 normally consists of a slender 

 stalk (filament) capped by an 

 enlarged part (anther), although 

 this stalk is often wanting. The 

 anther contains one, two or four 

 cavities (locules or "cells") in 

 which a powdery mass (pollen) is 

 located. The so-called cells are 

 not to be confused with the cells 

 of the plant tissue. The gynce- 

 cium and andrcecium, which are 



1515. Section of a flower 

 of corn-cockle. 



Showing torus, ovary, 

 styles, stamens and floral 

 envelopes. 



1519. Compound pis- 

 til of a St. John's-wort. 

 It has five carpels. 



1516. Parts of flower in 

 the trumpet-creeper. 



both necessary for the production of good seed, are 

 termed the essential organs of the flower. Ordinarily 

 each stamen represents one foliar unit. When many 

 stamens are present, this increase in number is brought 

 about in one of three ways : by an increase in the num- 

 ber of whorls of stamens (Caryophyllacese, Rosacese) 

 or an increase in length of the spiral (Ranunculus), by 

 the conversion of petals into stamens, or by a breaking 

 up of each individual stamen into many (St. John's- 

 wort). The first method is by far the most common. 

 In the last method, the origin is usually betrayed by 

 the aggregation of the stamens in fascicles. Normally 

 both filament and anther of each stamen is 

 free from its neighbors, but in some cases 

 the filaments are all joined into a tube 

 around the pistil (monadelphous) as in the 

 hollyhock, or into two groups (diadelphous) 

 as in the pea family. These two groups are 

 usually very unequal in the pea tribes, 

 nine stamens being united while the tenth 

 is free. In other cases the anthers may be 

 coherent while the filaments are free (synge- 

 necious), as in the Composite. In the Ster- 

 culiaceae, the filaments or tube of filaments 

 are variously toothed, crested or otherwise 

 modified; while in the Orchidacese they are 

 fused with the style to form the so-called 

 column or gynandrium of the flower. In 

 the milkweeds, each stamen bears a cornu- 

 copia-like appendage 

 which together form 

 the crown. In Viola, 

 two of the filaments 

 bear nectar-spurs. 



The anthers are 

 usually oval or oblong 

 bodies fixed to the 

 filament by the base 

 (basal), or by the 

 center (versatile). At 

 maturity they con- 

 tain normally two 

 1518. Head of simple pollen-sacs separated 

 pistils in hepatica. by a sterile tissue 



(connective) which is a prolongation of the filament. 

 The anther-sacs are sometimes four in number, some- 

 times reduced to one through fusion. The walls of the 

 sacs contain a peculiar fibrous 

 layer by the hygroscopic proper- 

 ties of which they are enabled to 

 curve back, thus opening the pol- 

 len-chamber along definite prear- 

 ranged lines and allowing the pollen 

 to escape. The dehiscence is usu- 

 ally by a longitudinal slit, but it 

 is frequently by terminal pores as 

 in the Ericaceae, or rarely by 

 transverse slits. In Vaccinium, the 

 pores are carried aloft on long 

 tube-like extensions of the anther, 

 while in Berberis the pores are 

 provided with an uplifting trap-door. 



The pollen-grains are normally spherical or oval cells 

 in which the two or three nuclei representing the male 

 gametophyte are found. The wall consists of a deli- 

 cate inner layer (inline), surrounded by a thicker 

 cutinized layer (exine) which is either smooth or 

 externally sculptured in various ways. Specialized 

 places in the extine serve as germ-pores through 

 which the pollen-tubes easily emerge. These 

 pores are sometimes provided with actual 

 lids (pumpkin and squash) which pop off at 

 the proper time. The pollen in the 

 Orchidaceae and Asclepiadacese is 

 more or less waxy and coheres into 

 one or several masses (pollinia). The 

 pollinia are in many cases produced 

 into minute stalks which connect with 

 a sticky gland that is designed to be- 

 come attached to visiting insects. On 

 the departure of the insect the gland, 

 together with the attached pollinia, 

 is carried away to the next flower. 

 The pollen-grains of orchids, heaths 

 and a few other plants are composed 

 of two to four cells (compound). 



Corolla (Figs. 1523-1527). Outside the stamens is 

 found a whorl of flat leaf-like usually colored organs 

 termed petals or collectively the corolla. The petals are 

 usually in one whorl and follow the numerical plan of the 

 flower closely; rarely are they fewer or numerous. They 

 are normally flat or concave colored bodies distinct 



1520. Anthers, 

 showing d e h i s- 

 cence; azalea on 

 left, barberry on 

 right. 



1517. 



Compound 

 pistil of 

 catnip. 



Showing 

 4-par ted 

 ovary, long 

 style, 2 stig- 

 mas (s). 



1521. Transitions from stamens to petals in the water-lily. 



from one another (polypetalous) and regularly spread- 

 ing from the receptacle. But in many plants the petals 

 are connate (gamopetalous) into one structure for a 

 greater or less distance toward the apices. The united 

 part is the tube, the lobed border the limb of the gamo- 

 petalous corolla. The lobes or segments are either all 

 alike and equally placed (regular corolla) or they vary 

 much among themselves (irregular corolla) . If the lobes 



