XVI 



POLLINATION AND FERTILISATION 



This description will do for most dimorphic plants, among 

 which the Primrose, Lungwort, and Common Flax are 

 examples. 



2. Trimorphic Plants. If a few flowers of the Purple 



Loosestrife are collected from different plants and examined 



'they will be found to be heterostyled, and in addition trimorphic, 



i.e., with styles of three different lengths. The arrangement of 



the styles and stigmas is seen from the following description : 



(A) Flowers, where the stamens are in two sets a short set 

 and a long set the 



top of the style 

 (stigma) coming 

 between the two. 



(B) Flowers, 

 where the stamens 

 are in two sets 

 one set of the same 

 length as the short 

 stamens in A, the 

 other of the same 

 length as the style 

 in A. The style is 

 longer than the two 

 sets of stamens. 



(C) Flowers, where the stamens are in two sets one set on 

 the same level as in the long style in B, and the other set level 

 with the style in A. The style is shorter than the two sets of 

 stamens. 



Thus, there are short-styles, medium-styles, and long- styles. 

 There are short-stamens, medium stamens, and long-stamens. 

 (Fig. 210). 



EXPT. 186. Collect flowers of the Purple Loosestrife from different 

 plants. They can be found in damp places in July and August. 

 Examine them. Note 



(i) The long tubular calyx, near the top of which the distinct, 

 crumpled, purple petals are inserted. 



(ii) The stamens inserted in the calyx tube, but much lower down 

 than the petals. 



(iii) The syncarpous (p. 186) pistil of two carpels, which possesses one 

 style and one stigma. 



Now dissect with care a number of the flowers, and arrange them 

 into three series according to the comparative lengths of the stamens 



P 2 



FIG. 210 Diagram of trimorphic forms of the 

 Loosestrife. 



