594 FLOWER 



which joins them, called thi- connecti 

 times is extensive, and in a few plants i 

 peculiar forms to aid in pollination, e. ; 



The sporangia at maturity consist 

 (rarely more) layers of oclls, coiistitul 

 rounding a quantity of ^|i"l' ~, ili< /. 

 portion of 



ells 

 thicke 



v'hos,. 



e. This some- 

 developed into 

 , in salvias. 



ns a wall, sur- 

 . » . The inner 

 ~ "f a layer of 

 I If irregularly 

 -■i that in dry- 

 iiir-inir it ntthe 

 I ",.;iI.:ti.'-s are 



the 





alo 



the 



at the junction of a pair of sporangia (the 

 left-hand groove in a, Pig. 831), which be- 

 come confluent, so that the dehiscent anther 

 may seem to have only two sporangia, when 

 it really has four. The pollen is thus 

 emptied out practically at once, though the 

 832. Anther break may begin at the top and progress to 

 of Azalea, the base. Examples: lilies, grasses. (6) The 

 Showing de- ^1'* "^^7 '^^ '^'''■y sl'oi't anfl e»pe widely, so 

 hiscence ii^^t a pore is formed through which the pol- 

 by pores, leu is gradually sifted ( Fig. 832). Examples: 

 the heaths, (c) In some plants the line of 

 breakage is curved, and the flap, 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 

 points. or is T;irionsl\- ridf^ed. In aneraoph- 

 ilous plants 1^1 r l'-ii,,',ilinn) the pollen is 

 dry and )Mi\\,lrr\ ; mi nTMiuophilous plants 

 it is usually moj-i ■n-l .•(.lierent. In milk- 

 weeds and orchid^ tln> whole of the pollen 

 from each sporangiiun is held together in 

 a mass by interwoven threads (Figs. 149, 

 513). By the time the sporangia discharge 

 the pollen, each spore has begun a develop- 

 ment which it completes on the stigma to 

 which it is transferred. See Fertilisatiort. 'Wiiiow. 



Cai-peZs. — The carpels are the sporangial Showing one 

 leaves which occupy the center of the compound 

 flower. The number of carpels is very pistil; s.stig- 

 variable. Usually they are fewer than the ™*= s(,style; 

 floral leaves. In most flowers the carpels "• '"'^'^• 

 are united one to another to form a structure known as 

 a compound pistil (Figs. 825, 833, 835, 836). When the 

 carpels are separate, each develops as a simple pistil. 

 Of these there may be one or many (Figs. 834, 837). 



The pistil, if simple, first appears as a ring-like 

 ridge about the center of the torus. If compound, knob- 

 like rudiments of the component carpels first appear, 

 but the growth early involves the torus between, giving 

 rise to an elevated circular ridge. This carpellary ring 

 irradnnllv irrows upward, partially or completely inclos- 

 ing one or more chambers, in 

 which the ovules arise. At a time 

 when the ovules ( which ripen into 

 seeds) were supposed to be com- 

 parable to the eggs of animals, 

 the larger chambered part of the 

 pistil in which they are formed 

 was called the ovary, a name 

 which it still retains in descrip- 

 tive botany. The pistil is often 

 prolonged above the ovary. This 

 part is the style. 



• «P" 





{nuceUiis). Witliin 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 



three -chambered 



FLOWER 



section of the sporangium appears as a cavity with- 



tissue which surrounds it. It later 



becomes the so-called embryo sac, 

 within which occurs the process of 

 fertilization (which see). 



The ovules conmionly arise upon 

 ■irtain lines or ridges which project 

 into the pistil chamber, more rarely 

 upon the whole interior surface of the 

 ovary. These lines or ridges are called 

 placenta. See Figs. 825, 835, 8:f7. 

 . ,., , - ,. In a simple pistil there is usually but 



Pistil ol Tulip, one placenta (Fig. 837). In a compound 

 i?i7nf „ .TI'^J P'**'"' ^^^ "°'™ "^ ^'"^ carpels may be 

 such as to produce a l-chambered 

 ovary, or the ovary may contain as 

 many chambers as there are carpels 

 (Fig. S.'l.'il. In the former case the placentas will project 

 iii\v,ir.l I'l-iii til.' Miill .if tli.' .iMir\ : in the latter they 



tip. : :.|.-. .•■ ..ll'" , I., !■ ■., ;i ,', h ; , I ,l I h ■ r,s of 



qini'' r r tlicir attachment, as iu the 



p"! . ' : I I I" I ^ee also Fig. 837). 



I: iiilile number of plants the 



o\iiI.- ,111-. lip.n 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 (Fig. 833). Its 

 length and form are adapted to the means by 

 which the pollination of the pistil is secured. 

 In some cases the style is practically wanting. 

 Its interior is occupied by a tissue whose 

 cells are pushed aside and partly digested 

 l)y the growing pollen tube (see I'ertili- 

 2ation). It is not infrequently traversed by 

 a canal, a prolongation of the ovule chamlx r. 



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, 536. com- 

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

 stigma (Figs. 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. In othercases the style is elongated, style.2stie- 

 and the receptive surface is a long line upon ™*^ ^"' ■ 

 one or more sides of the elongated style. In other cases 

 the style is much branched, as in the grasses, and these 

 branches constitute the stigma. At the time the pollen 

 is being discharged, the stigmatic surfaces are often 

 covered by a sticky secretion. AH of these devices are 

 adaptations to insure the lodgment, adhesion and nutri- 

 tion of the pollen spores (see Pol! in 11 linn). 



The stimulus resulting from fi rtiUzation 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 Reid Barnes. 



