Oct. 1, 1S70.1 



HARDWICKE'S SCIENCE-GOSSIP. 



221 



wards, and strewn over the surface of, the [ocean 

 until they sank, and were buried in the deposits 

 accumulating along the bottom, where the bony- 

 scaled and shagreen-skinned little fishes were living, 

 breeding, and dying. 



} My story is now finished, for the formation of 

 cracks and fissures in our solid rocks belongs to a 

 later time. Of the minerals and metals which were 

 segregated along the walls of these fissures until 

 the latter became " metal lodes," I cannot say ; but, 

 thus much — that, apart from the numerous fossils 

 contained in us, our rocks will always be esteemed 

 interesting to man, seeing that it is iu them that 

 gold is most abundant. 



ON DIMORPHISM, OR THE OCCURRENCE 

 OF DIFFERENT FORMS IN CERTAIN 

 PLANTS. 

 By F. I. Warner* 



l~N studying any branch of natural history it is 

 -*- exceedingly interesting to notice the various 

 contrivances by which the same general law is ap- 

 plied to particular cases. Nature is in her laws 

 uniform aud consistent, however modified those 

 laws may be in some instances, and however varied 

 their mode of application. It has been enunciated 

 by Mr. Darwin, aud is, I believe, very generally 

 held by naturalists and physiologists, as a maxim 

 or general law, that nature abhors perpetual self- 

 fertilization, and that with all organized beings 

 distinct individuals must at least occasionally inter- 

 cross. That this is an universal law in the animal 

 kingdom no one doubts ; its application, however, 

 to the vegetable kingdom is not so generally known 

 or held. No one, however, acquainted with the 

 researches of Darwin, Gartner, Sprengel, and others, 

 who have given the subject their attention, can 

 refuse his assent to its being of at all events very 

 general application. 



The contrivances by which the intercrossing of 

 distinct individuals is insured in the case of plants 

 are very various, and many of them excessively 

 beautiful. One of these contrivances is that by 

 which a species is separated into two or more forms 

 differing in the structure and function of the pistils 

 and stamens, and each form depending on another 

 form for complete fertilization. This has been 

 designated by Mr. Darwin, who was the first to 

 point out its meaning, reciprocal Dimorphism. 



If a number of primroses or cowslips be gathered, 

 even from the same bank, and growing side by side, 

 two distinct forms will be found nearly equally 

 distributed amongst the flowers ; some will have 

 the pistil appearing just inside the throat of the 



* Paper read before the Winchester and Hampshire Scien- 

 tific and Literary Society, June, 18/0. 



carolla, the stamens being out of sig^it about half- 

 way down the tube ; the others will have the sta- 

 mens appearing, being attached by their very short 

 filaments just within the mouth of the tube, while 

 the pistil is out of sight, occupying the position of 

 the anthers in the other form. This difference in 

 form, or dimorphism, is a very general characteristic 

 of the sexual organs in the different species of 

 Primula, and occurs also in several other genera of 

 the same order, and is well-known to polyanthus 

 and auricula fanciers, who designate the long-styled 

 forms "pin-centres" or " pin-eyed," and the short- 

 styled forms, " rose-centres " or " thumb-eyed." 



The two forms differ in other respects : the ex- 

 pansion in the tube of the corolla is much longer in 

 the long-styled than in the short-styled form, owing 

 to the difference in the position of the anthers. The 

 stigma in the long-styled flowers is always more or 

 less globular and very rough, whereas in the short- 

 styled flowers the stigma is nearly always flattened 

 or depressed on its summit, and much smoother. 

 The pollen-grains iu the long-styled form are smaller 

 and more oblong than in the short-styled. The 

 difference in position of the anthers might, at first 

 sight, appear to arise from, or to be connected with, 

 the fact, that in plants belonging to the Primrose 

 family, there is a suppression of a whorl of stamens, 

 or at all events of some kind of floral leaves. That 

 this is the case is seen from the stamens in plants of 

 this order being opposite to the petals or lobes of 

 the corolla, and not alternate, as in other flowers ; 

 and it might be imagined that in the long-styled 

 form a whorl of long stamens, and in the short- 

 styled form a whorl of short stamens had been 

 suppressed. This, however, if true, does not explain 

 the fact that in loth the existing forms the stamens 

 are opposite, nor does it explain the difference in 

 length of the pistil. 



In addition to the structural differences I have 

 mentioned, there are very remarkable functional 

 differences between the two forms. The first per- 

 son who pointed out these was Mr. Darwin, whose 

 experiments are most interesting, and fully con- 

 firmed by those of subsequent observers ; among 

 other experiments he covered up with net six short- 

 styled and eighteen long-styled cowslips, aud found 

 that the former produced from twenty-four umbels 

 of flowers, 1-^ grains of seed, or fifty seeds ; and the 

 latter from seventy-four umbels not a single seed. 

 Judging from plants growing in the same bed and 

 unprotected from insects, the six short-styled plants 

 ought to have produced ninety-two grains weight 

 of seed instead of only 1 ^ , aud the eighteen long- 

 styled plants instead of not one seed should have 

 produced two hundred grains weight. These and 

 similar experiments prove that the visits of insects 

 are necessary to the fertilization of the different 

 species of Primula, all being more or less sterile 

 when protected from such visits. Further experi- 



