594 



FLOWER 



which joins them, called the coinuctire. This some- 

 times is extensive, and in a few plants is developed into 

 peculiar forms to aid in pollination, e. g., in salvias. 



The sporangia at maturity consist of two ^r four 

 (rarely more) layers of n-Us, cunstitutinK a wall, sur- 

 rounding a quantity '■( -I iir .iIm /'/.)/. Th.- iiiiifi- 



portion Ol' l!i> ; l .■ .: i -l - ..r ;, l:i\ .1- of 



^V'S thickened. ii-iKill, i:i Inuicl-. ^.. tint m dry- 



p.. I ing they warp tin- wall, rupturing it at the 



tt .'^a weakest place. The lines of weakness are 



i^^i'^'i] usually definitely localized, so that each an- 



(|;if; y ther breaks in a regular way. (rt ) The nip- 



the nnth('T. In tl,:M '^r , -, ,1 ',■ .', ,,,,i i,. , 



it really has four. "The pollen is thus 



emptied out practically at once, thou^^li ilif 



832. Anther l^''"* "">■ ''«-'" "* "'" *"'P *""> progrtss tii 



oiAzalea. thrli.i ., I , >.., ,„ , ,1, - I ili. ^. -rasses. ( 6) The 

 Showingde- sli. ,:.. ^. i 'I I M i;ape widely, -~ 



by pores, h-ri i - - i .m u.i li ^ ~ i : . ■ .i 



breakage is curved, and the Hap, so re- 

 leased, bends outward on drying, lifting 

 like a hinged lid, and closing again in 

 dampness. Examples: Mahonia, barberry, 

 cinnamon. 



The pollen spores are, at maturity, sin- 

 gle cells, each with a rather thick wall, 

 which is often studded with bosses, or 



which the pol- 

 12). Examples: 

 nts the line of 



In I 



ilk- 



weeds ami oiirhids ilii.: tthulo of the pollen 

 from each sporangium is held together in 

 a mass by interwoven threads (Pigs. 149, 

 513). By the time the .sporangia discharge 

 the pollen, each spore has liegun a develop- 

 ment which it rM.ni|>Iftcs ou the stiL:-ina to 

 whichitistraii-.lVnv,l. s, ,■ /.;,■/,/,;„/,„». 



Carpels. — T\<' .arpd-. ai-r ilir ~|i.ii-,iiL:ial 

 leaves which occupy the ccutcr uf the 

 flower. The number of carpels is very 

 variable. Usually they are fewer than the 

 floral leaves. In most flowers the carpels "' °™'^- 

 are united one to another to form a structure known a 

 a compotmd pistil (Pigs 825, 833, 835, 836) When th 



rpels are separate, each develops as a simple 



833. Pistillate 

 flower of 

 Willow. 

 Showing one 

 eomponnd 

 pistil: s. stig- 

 ma: s(.style; 



Of these there may be 

 The pistil, if simpl 

 ridge about the centf i 

 like rudiments of tli 

 but the growth earlj i r 

 rise to an elevated cii 

 gradually grows up^^ o 



(Pigs 834, 837) 



tne botinv The pistil is i tteu 

 ) rolongi d above the ovar\ This 

 1 art IS the -.tijh 



Anovuleisafleshj sporangium, 

 lacketed by one or two (larely 

 three) outgiowths from the base, 

 the mteijuments, which almost 

 inclose the sporangium proper 

 {nucellHs). Within the sporan- 

 gium of the ovule, several (1 to 40) spores begin to de- 

 velop. Of these, however, rarely more than one reaches 

 maturity. This spore is never set free as the pollen 

 spores are. It therefore acquires no thick wall, and in a 



FLOWER 



section of the sporangium appears as a cavity with- 

 in the delicate tissue which surrounds it. It later 

 becomes the so-called embryo sac, 

 within which occurs the process of 

 '/f\!rt(\ fertilization (which see). 

 V. ^ ,\ The ovuhs commonly arise upon 



■ri:ijii liiiis or I'idges which project 

 :to the pi-til chamber, more rarely 

 p.. 11 tlic wloih- interior surface of the 

 .'ary. These lines or ridges are called 

 835. Section across i/lncentu:. See Figs. 825, 835, 837. 

 the compound Jq a simple pistil there is usually but 

 pistil of TuUp. one placenta ( Fig. 837). In a compound 

 Showing central pistji the union of the carpels may be 

 Fi,„5^^„ v,?"'i such as to produce a 1-chambered 

 .hr«.chambered ^^.^^^^ ^^ the^vary may contain as 

 many chambers as there are carpels 

 (Pig. 835). In the former case the placentte will project 

 iiiw iiiil from the wall of the ovary ; in the latter they 

 will lie aggregated at the center, from which 

 the\ iiiiiy project outward into the chambers of 

 the ovary. When theovules are numerous, the 

 placentte are often enlarged to form an ade- 

 quate surface for their attachment, as in the 

 potato and tomato (see also Fig. 837). 



In a considerable number of plants the 

 ovules arise upon the torus itself, a ring of 

 which grows upward, cup-like. From the 

 edge of this cup arise the floral and sporangial 

 leaves, the ovules developing on its sides or 

 base. The carpels then form a mere roof over 

 the ovule chamber. 



The style is sometimes slender and very 

 long (up to several inches; see Fig. 836); 

 sometimes short and thick (Pig. 833). Its 

 length and form are adapted to the means bv 

 which the pollination of the pistil is secured. 

 In some cases the style is practically wanting. 



cells are pushed aside and partly digested 

 by the growing pollen tube (see Fertili- 

 siitinii). It is not infrequently traversed by 

 a caiuil, a prolongation of the ovule chamber. 



(some portion of the style, or when that is 

 wanting a portion of the outer surface of the 

 ovary itself, is adapted to the reception of 

 the pollen .spores. This receptive surface, 835. com- 

 whatever its form or location, is called the pound pis- 

 stigma (Pigs. 833,836). In many cases the tilof catnip, 

 upper part of the style is enlarged into a Showing 

 knob or club-shaped or lobed portion, the 4-parted 

 area of the receptive surface being thus in- ovary.long 

 creased Inothercasesthestvleisdongated style.Sstig- 

 and the receptive surface is a long line upon """* ^"• 

 one 01 more sides ot the elongated st\ le In other cases 

 the st\ le IS much brmched, as m the grasses, and these 

 1 rin hps constitute the stigma At the time the pollen 

 I 11 ^ disthaiged the stigmatic surfaces are often 

 1 I 1j% a sticks secretion All of these devices are 



I 1 It I >ns to insuie the lodgment adhesion and nutri- 

 ti 11 t the pollen spores (see Pollination) 



837 Section ilfi 

 Showing VI, 



The stimulus resulting from fertilization often accel- 

 erates the growth of the pistil or causes it to resume 

 growth if it had ceased. The various changes in size, 

 texture, color, etc., result in the production of fruit. 

 Charles Reiu Barnes. 



