RELATION OF MORPHOLOGICAL NATURE OF ORGANS TO ADAPTATION. 84I 



in the hop, dahlia, and bryony. In bulbs again the reserve accumulates in the leaves 

 (bulb-scales) which surround the bud that developes into the new plant. The 

 reserve often collects in cataphyllary leaves of peculiar development; in Allium Cepa 

 in the lower part of the leaf-sheaths, which persist through the winter, while the upper 

 parts of the leaves die off. 



We have already in the last chapter spoken of the immense variety of the 

 contrivances which have for their object the partial or entire prevention of the 

 self- fertilisation of plants, in order to produce a stronger and more numerous off- 

 spring by the sexual union of different individuals ; and only a few examples need 

 now be mentioned. Since the form, size, colour, position and movements of the 

 parts of the flower are almost invariably adapted to facilitate the conveyance of 

 pollen from one flower to another, generally by insects, and often even to render 

 self-fertilisation impossible ; and since a great diversity even of those forms of flowers 

 which are constructed on the same morphological type results from this, so the 

 properties of ripe seeds and fruits are no less adapted^ to bring about the disse- 

 mination of the seeds. Fruits which are very similar from a morphological point of 

 view may nevertheless assume physiological properties which are altogether different, 

 and fruits which are very different morphologically may become extremely similar in 

 consequence of their adaptation to the purposes of dissemination. The service 

 rendered by insects in the fertilisation of diclinous, dichogamous, dimorphic, and 

 many other flowers, is performed by birds in the dissemination of a number of seeds 

 which are concealed beneath fleshy edible pericarps ; in some cases, as the mistletoe, 

 it is scarcely possible to imagine any other mode of dissemination than the eating of 

 the berries by birds. Dry fruits or the seeds which are shed by dry fruits are 

 often provided with an apparatus adapted for transport by the wind, the morpho- 

 logical value of which is as various as possible. The wings on the seeds of species 

 of Abies are a superficial layer of the tissue of the scale (carpel), those on the seed 

 of Bignojiia muricata originate from the integument of the ovule ; the wings of the 

 indehiscent fruits (samarse) of Acer, Ulmus, &c., are outgrowths of the pericarp ; the 

 crown of hairs on the seed of Asclepias syriaca evidently performs a similar service ; 

 as does the pappus of many Compositse which is a metamorphosed calyx. In these 

 cases it is obvious that the wind carries the seeds or fruits ; in other cases animals 

 of considerable size perform this office involuntarily, the hooked or rough fruits 

 becoming attached to them and afterwards falling off^. 



In most of these adaptations, both their purpose and the mechanical con- 

 trivances for its attainment are easily recognised; but not unfrequently the latter 

 require a closer examination and some reflection in order to understand them. 

 Among many other cases of this kind one only may be mentioned here which 

 any one can easily observe for himself. The fruit of Erodium grm'num and other 

 Geraniacese^ splits up into five mericarps each of which has the form of a cone with 



1 It is scarcely needful to mention again that this mode of expression has only a metaphorical 

 meaning from the stand-point here assumed, and is only used for the sake of convenience. 



- [A remarkable instance of this is recorded by Dr. Shaw (Journ. Linn. Soc. vol. XIV, 1874, 

 p. 202), in the introduction into South Africa and enormously rapid distribution of a European 

 plant, Xanthium sphwsiim, by the spiny achenes clinging to the wool of the Merino sheep.— Ed.] 



3 See Hanstein, Sitzungsber. der niederrheinischen Ges. in Bonn, 1868. 



