126 



PLATSTT RELATIONS. 



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

 devices used by 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 the flower, makes it un- 

 likely that the pollen will fall upon the 

 stigma. The stigma may be placed 

 above or beyond the pollen sacs, or the 

 two may be separated by some mechan- 

 ical obstruction, resulting in much of 

 the irregularity of flowers. 

 PIG. 132. A portion of In the flowers of the rose acacia and 



the flower of an iris, iis re i at i v es, the several stamens and 



or flag. The single . . 



stamen shown is the Single Carpel are in a Cluster, en- 

 standing between the closed in the keel of the flower. The 



petal to the right and . 



the petai-iike style to stigma is at the summit of the style, 

 the left. Nearlhe anc [ projects somewhat beyond the 



top of this style the ,, ... 



stigmatic shelf is pollen-sacs shedding pollen. Also there 

 seen extending to the ig often a rosette of hairs, or bristles, 



right, which must , -, ,-, ,-, ,. i i 



receive the pollen J ust beneath the stigma, which acts as 

 upon its upper sur- a barrier to the pollen (see Fig. 131). 



In the iris, or common flag, each 

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



stamen While ob- the tal and the petal _ like gtyle while 

 taming the nectar the * t - 1 * 



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

 pollen-bearing part fl ap ^ or ghelf, which the style sends out 



of the stamen, and rn ^ 



pollen is lodged upon as a root to the pocket. With such an 

 its body, in visiting arrangement, it would seem impossible 



the next flower and ,, ,, , ,, , . 



entering the stamen for the pollen to reach the stigma un- 

 stig- aided (see Fig. 132). 



In the orchids, remarkable for their 

 strange and beautiful flowers, there are 



" Tu'n" 



chamber the 



GRAY. 



