PRIMULACEAE 



65 



Fig. 239. Diagram of the Legitimate and Illegitimate 

 Unions possible in Primula (after Charles Darwin). The 

 legitimate unions are indicated by horizontal dotted lines, 

 and the illegitimate ones by curved ditto. 



These results were confirmed by the investigations of Hildebrand, who further 

 proved that when flowers were artificially self-pollinated fertility was at a minimum. 

 By sowing separately the seeds resulting from the different kinds of union, 

 Hildebrand found that when both parents were long-styled the offspring were 

 predominatingly so, and similarly for short-styled stocks. Crosses between the 

 two kinds of stock resulted in off- 

 spring which were long- and short- ^~\ ^. .^ 



styled in approximately equal pro- 

 portions. 



The researches of Darwin and 

 Hildebrand threw entirely new light 

 on the significance of crossing and 

 sexuality in general. 



1813. P. elatior Hill. (Herm. 

 Miiller, 'Fertilisation/ pp. 384-5, 'Al- 

 penblumen,' p. 369, ' Weit. Beob.,' HI, 

 pp. 64-5 ; Schulz, ' Beitrage,' II, 

 pp. 145-6; Kirchner, 'Flora v. Stutt- 

 gart,' pp. 533-4 ; Knuth, ' Bloemen- 

 biol. Bijdragen '; MacLeod, Bot. Jaarb. 

 Dodonaea, Ghent, v, 1893, pp. 

 444-6.) This species bears hetero- 

 stylous flowers belonging to class 

 HhL, which do not attain their full 



size till towards the end of anthesis. The corolla is of pale-yellow colour with 

 a yolk-yellow throat, and its tube differs in length and shape in the long- and short- 

 styled forms. 



(a) brachystyla: corolla-tube 15-17 mm. long, gradually narrowing to a little 

 distance (3-5 mm.) below the horizontally expanded limb, and then at a level of 12-13 

 mm. from its base enlarging again. The five anthers, borne on filaments with wider 

 bases, are situated in this enlarged region, and they extend to the opening of 

 the tube, where their tips converge. The pollen-grains are about twice as large 

 as in (b). The relatively thick style is about half the length of the corolla-tube ; the 

 stigma is broader than deep, and beset with short papillae. 



(b) macrostylai corolla-tube 12-14 n^"^- long, widening somewhat in the 

 middle where the stamens are inserted, and then gradually narrowing again. 

 The pollen-grains are only about half as large as in (a). The style is tolerably thin 

 in its upper part, and so long that the spheroidal stigma is situated in the entrance of 

 the flower. The stigmatic papillae are about five times as long as those of (a). 



The two kinds of flowers are about equally frequent, and borne on separate 

 stocks. 



Humble-bees probing for nectar in the legitimate way touch the organs in the 

 entrance of the flower with their heads, and those in the middle of the corolla-tube 

 with their laciniae. The regions in question consequently get dusted with pollen, 

 which is transferred to stigmas situated at the same level in the other kinds of stocky 



DAVIS. Ill F 



