ON FRUITS AND SEEDS. 



167 



thus hurls the seeds to some distance, being even itself sometimes also 

 torn away from its attachment. 



Other cases of projected seeds are afforded by Sura, one of the 

 Euphorhim, Collomia, Oxalis, some species allied to Acanthus, and by 

 Arceuthohium, a plant allied to the mistletoe, and parasitic on juni- 

 pers, which ejects its seeds to a distance of several feet, throwing them 

 thus from one tree to another. 



Even those species which do not eject their seeds often have them 

 so placed with reference to the capsule that they only 

 leave it if swung or jerked by a high wind. In the 

 case of trees, even seeds with no special adaptation 

 for dispersion must in this manner be often carried 

 to no little distance ; and to a certain, though less 

 extent, this must hold good even with herbaceous 

 plants. It throws light on the (at first sight) curious 

 fact that in so many plants with small, heavy seeds, 

 the capsules open not at the bottom, as one might 

 perhaps have been disposed to expect, but at the 

 top. A good illustration is afforded by the well- 

 known case of the common poppy (Fig. 11), in 

 which the upper part of the capsule presents a 

 series of little doors (Fig. 11, a), through which, 

 when the plant is swung by the wind, the seeds 

 come out one by one. The little doors are protected 

 from rain by overhanging eaves, and are even said 

 to shut of themselves in wet weather. The genus 

 Campanula is also interesting from this point of fig. 11. Seed-head op 

 view, because some species have the capsules pen- oppyc ajtaver. 

 dent, some upright, and those which are upright open at the top, 

 while those which are pendent do so at the base. 



In other cases the dispersion is mainly the work of the seed itself. 

 In some of the lower plants, as, for instance, in many sea-weeds, and in 

 some allied fresh-water plants, such as Vaucheria, the spores * are cov- 

 ered by vibratile cilia, and actually swim about in the water, like in- 

 fusoria, till they have found a suitable spot on which to grow. Nay, 

 so much do the spores of some sea-weeds resemble animals, that they are 

 provided with a red " eye-spot " as it has been called, which, at any 

 rate, seems so far to deserve the name that it appears to be sensitive 

 to light. This mode of progression is, however, only suitable to water- 

 plants. One group of small, low-organized plants {Marchantia) develop 

 iamong the spores a number of cells with spirally thickened walls, 

 which, by their contractility, are supposed to disseminate the spores. 

 In the common horse-tails {Equisetum), again, the spores are pro- 

 vided with curious filaments, terminating in expansions, and known 



* I need hardly observe that, botanically, these are not true seeds, but rather motile 

 buds. 



