V EG ETA TIVE REP ROD UCTION. 



207 



by lines and spots, seem to be dependent upon the relation 

 of the flower to insects. (See further \ 390.) 



Fig. 168. Fig. i6g. 



Fig. 168. — A flower of the flax, halved ; showing radial symmetry. See fig. i6g. Mag- 

 nified 2 diam. — After Bessey. 



Fig. 169. — Diagram showing the arrangement of the parts of a flower of flax. Outer 

 circle, 5 sepals ; second, 5 petals ; third, 5 stamens ; fourth, 5 carpels, each divided by 

 a false partition into 2 chambers. Five different radial planes will, therefore, divide 

 this flower into halves.— After Bessey. 



295. Pollination. — To bring about the forn:iation of a 

 new plant within the ovule the pollen spores must lodge near 



Fig. 170. Fig. 171. 



Fig. 170. — An unopened flower of the sweet pea, halved ; showing bilateral symmetry 



(irregularity). Slightly enlarged. — After Bessey. 

 Fig. 171. — Diagram showing the arrangement of the parts of the flower of sweet pea. 



Outer circle^ calyx (5-lobed) ; second, 5 petals, the two lower united ; third, ic stamens, 



g united by filaments, i separate ; center, one carpel. Only one plane will divide this 



flower into halves.— After Bessey. 



the ovule and develop. To insure this a portion of the pistil 

 forms a receptive surface, the stigma, to which the pollen 

 spores readily adhere. It is advantageous, also, to have the 



