120 



I'LANT STUDIES 



out of the i3ollen-sacs or to be removed from them. The 

 devices used Ly flowers containing both stamens and carpels 

 to prevent self-pollination are very numerous, but most 

 of them may be included under the three following heads : 

 (1) Position. — In these cases the 

 pollen and stigma are ready at the same 

 time, but their position in reference to 

 each other, or in reference to some con- 

 formation of tlie flower, malves it un- 

 likely that the pollen will fall upon the 

 stigma. The stigma may be placed 

 al)ove or beyond the pollen sacs, or the 

 two may be separated by some mechan- 

 ical obstruction, resulting in much of 

 the irregularity of flowers. 



In the flowers of the rose acacia and 

 its relatives, the several stamens and 

 the single carpel are in a cluster, en- 

 closed in the keel of the flower. The 

 stigma is at the summit of the style, 

 the left. Near the .nn^ projects somewluit bcvond the 



top of this style the ,, i it ii \^ ^^ 



pollen-sacs shedding pollen. Also there 

 is often a rosette of hairs, or bristles, 

 just beneath the stigma, which acts as 

 a barrier to the pollen (see Pig. lol). 

 In the iris, or common flajj, each 



Fig. 133. A portion of 

 the flower of an iris, 

 or fliig. The single 

 stamen shown is 

 standing between the 

 petal to the right and 

 the petal-like style to 



stigmatic shelf is 

 seen extending to llie 

 right, which must 

 receive the pollen 

 upon its upper sni-- 

 face. Tile nectar 

 pit is at the junc- 

 tion of the petal and stamen is in a sort of pocket between 

 stamen. While oh- ^j^^ ^^.^j .^,^^| jj^^. petal-like stvle, while 



tainmg theueetar the -"- -*- 



insect brushes the the stigmatic siirftice is on the top of a 



pollen-bearing part j|.^|,_ qj. s]j(,]f_ ^^.l);,.], ^1,^, gf^.jg g^,,,^^^ „„^ 

 of the stamen, and 



pollen is lodged upon i's :i roof to the jiocket. AVitli such an 

 its body. In visiting arrangement, it would seem impossible 



the next flower and „ . .. i ii 



entering the stamen i'^^' the poUeii to reach the stignui un- 

 chamber the stig- aided (sec Fig. IIS'-^). 



matic shelf is ant. to ^ ,, "^i-n iiii. ,-,. 



be brushed. -Afier ^'^ the orcliids, remarkable for their 



Gray. strange and beautiful flowers, there are 



