COTYLEDONS. 



crust again becomes changed into a mucilaginous adhesive mass which glues 

 them to the substratum. The whole succulent decaying pericarp often becomes 

 the fixing agent of the seeds, as, for example, in gourd-like plants, and in many 

 plants with berries and stone-fruits. 



In numerous plants, e.g. in the Corn-cockle (cf. figs. 141 7 > 8 > 9 ' 10 ), and in 

 Neslia paniculata which grow abundantly in loamy fields, the fixing of the 

 fruits or seeds to the soil is not effected by mucilaginous cement-materials, but 

 by inequalities on the surface of the integument. Here are developed extremely 

 diversified warts, pegs, ridges, or net-works, and between them pit-like depres- 

 sions into which the earth - particles penetrate, and when moistened become 

 closely connected with the superficial cells. The adhesion is therefore very 

 close, and if we try to cleanse these seeds or fruits, and to remove the clinging 

 soil from all the small hollows, we shall not completely succeed even after a 

 great deal of trouble. And here we must point out the interesting distinction 

 between rugged seeds like these, and such as become slimy. Seeds with rough, 

 wrinkled, and pitted surfaces never develop adhesive agents, since they are fixed 

 to the soil by these inequalities of the seed-coat; on the other hand, seeds with 

 smooth surface, which would otherwise be easily displaced, adhere by means of 

 mucilage developed by their epidermal cells. 



The Water-chestnut (Trapa), whose germination was described on p. 609, 

 behaves in a very peculiar manner. Each of its large fruits exhibits two pairs 

 of projecting spines arranged cross- wise, which have been formed from the 

 sepals, and which protect it during ripening from the attacks of aquatic 

 animals. These spines, as well as the whole fruit, are as hard as stone, but 

 only in the interior. The outer cell-layers are soft, decompose quickly under 

 water, and separate from the deeper tissue in irregular tatters and shreds. 

 At the apex of the spines, after the detachment of the soft portion there 

 remain not only the strong hard midrib, but also the commencements of some 

 recurrent bundles of very firm elongated cells which spring from the midrib 

 immediately behind the apex. These spines therefore have the appearance of 

 anchors (see fig. 146), and indeed they function as anchors, adhering at the 

 bottom of the lake by means of their barbed points to various vegetable 

 remains which cover the mud, and are actually anchored there. The seedling 

 arising from the nut does not consequently lift the pericarp with it, but this 

 remains fixed in the place where it fell. 



Peculiar contrivances for anchoring fruits to spots suited for germination are 

 observed in many steppe-grasses, especially in the Feather-grass (Stipa) and in 

 the Stork's -bill genus (Erodium). The feather-grasses are a striking feature 

 of steppes; indeed, together with various Papilionacese especially with tragacanth 

 shrubs (Astragalus) and with numerous Composite, pinks, and low irises, they 

 compose the chief constituent of the vegetation. The appearance of the Feather- 

 grass is appropriate to its name, consisting as it does of tufts of white feathery 

 streamers swinging in the wind. This characteristic feature makes its appearance 



