HETEROSTYLY 



45 



I do not think that this is a chance arrangement, but an adaptation of Nature, 

 though I am not now in a position to indicate the object of it.' Sprengel was 

 therefore acquainted with Dimorphism ^ but its significance was first made clear 

 by Darwin (see p. 8). Vaucher was the first to observe the Trimorphism of Lythrum 

 Sahcaria (1841, Hist. phys. des plantes d'Europe, II, p. 341), and it was afterwards 

 noticed by Wirtgen (Verb. d. naturh. Ver. fiir Rheinl. und Westfalen, v, 1848, p. 7). 



In the large majority of cases Heterostyly is associated with other differences 

 between the two forms of flower than unequal length of style and stamens. In 

 dimorphous flowers, for example, the pollen-grains of the long-styled flowers are 

 considerably smaller than those of the short-styled ones, while the stigmatic papillae 

 of the former are considerably longer than those of the latter. 



Fig. 3. Primula acauli's, /acq., a plant with dimorphous flowers. (Longitudinal section) 

 twice natural size. 



(2) Short-styled form. 



Relative sizes of pollen-grains 



(3) Of the short-styled form. 



(4) Of the long-styled form. 



5 



6 



Relative sizes of stigmatic papillae 



(5) Of the long-styled form. 



(6) Of the short-styled form. 



[(3) -(6) Highly magnified.] 



In some cases of dimorphism there is also a noticeable dissimilarity between the 

 two forms of flower in regard to size and conspicuousness. The long-styled flowers 

 of Primula longiflora and minima, for example, possess a larger and more conspicuous 

 limb to the corolla than the short-styled, while in Primula auricula and glutinosa the 

 opposite is the case. In the former two species the short-styled flowers are capable 

 of self-pollination, as are the long-styled ones of the other two. Kerner, after 



* According to Loew, ' Einf. in d. BlUtenbiologie ' (p. 55, note). Dimorphism was discovered 

 almost simnltaneously by Sprengel, W. Curtis (' Flora Londinensis,' I. Edit. 1777-87), and Persoon 

 (Usteri's Annalen, 1794, Part 2). The last two both made the discovery in Primula. 



