324 rur^f ifosi: fiowkus. 



protrndino- head is the female reproductive organ or stigma, 

 and flowers of this kind are known as pin-centres. 



Now at the first glance, looking at these two very dissi- 

 milar forms, it woidd be natural to suppose that the Primrose 

 is a dioecious plant — some specimens being male and some 

 female ; but this is not the case, for all the flowers are 

 hermaphrodite, and capable of producing seed. The difference 

 lies in the position of the stamens and the relative length of 

 the style. In the pin-centres the style is comparatively long, 

 carrying the stigma right up to or even beyond the mouth of 

 the corolla, Avhile the stamens are inserted on the lower half of 

 the tube, and thus are placed too low down to be visible. In 

 the rose-centres, on the other hand, the stamens are situated 

 almost at the very top of the corolla-tube, and at the same 

 time the style is comparatively short, not more than perha])S 

 one-third of the length which it measures in the long-styled 

 variety. This peculiar difference in the relative position of 

 the reproductive organs — technically known as heterostyly — 

 is a wonderful provision of nature for ensuring the fertiliza- 

 tion of species, and although a very imcommon contrivance, 

 is not restricted to the Primrose, nor to the Primulaceai in 

 general, but also occurs in plants belonging to other orders. 



As the flowers of the Primrose usually grow on erect or 

 slightly inclined stems, it is evident that the stamens in a 

 rose-centred individual occupy precisely the right position to 

 ensure self-fertilisation ; because when once the anthers are 

 mature, any sudden shock given to the flower by some passing- 

 object, or even by a gust of wind or a shower of rain, will 

 suffice to send down a shower of pollen upon the stigma 

 below. But in the pin-centred flower a similar shock would 

 produce a negative result, since the stigma towers far above 

 the anthers ; consequently the pollen Avould fall to the bottom 

 of the tube, and be w^asted, unless some other mode of utilis- 

 ing it were employed. Obviously therefore this arrangement 

 is not conducive to self-fei'tilisation, and so the plant has to 

 depend for its propagation on the agency of insects. A bee 

 or a fly having just visited a rose-centred primrose in search 

 of honey, could not fail to have its head and thorax dusted 

 over with pollen from the ripe anthers, and on its arrival 

 afterwards at a pin-centred blossom, some of it, even a few 

 grains, would be deposited on the projecting stigma, and thus 

 quite involuntarily and unconsciously cross-fertilisation would 

 be brought about. 



It would appear therefore that the heterostyled flowers 

 of the common Primrose offer two alternatives for the fructifi- 



