SCIENCE-GOSSIP. 



43 



was a sound conclusion of Darwin, and one, as he 

 remarked, that is in accordance with the common 

 experience of gardeners. Thuret, in fact, after 

 experimenting on the buoyancy in sea-water of the 

 seeds of about 250 species of plants, belonging to 

 seventy-seven families and to various regions, 

 found that not over two per cent, had any powers 

 of flotation, all the rest sinking at once or in a 

 few days (" Archir. des Sci. Phys. et Nat." tome 47, 

 1873). Upon the seeds of the great majority of 

 plants that I experimented on, prolonged drying 

 had but a slight influence. Seeds that sink at once, 

 in the mature and fresh condition, rarely gain 

 much buoyancy after 

 drying for a year. 



The 273 species ex- 

 amined comprise 20S 

 dicotyledons belonging 

 to fifty families, and 

 sixty-five monocotyle- 

 dons belonging to 

 twelve families. Of 

 the 210 species, where 

 sinking took place at 

 once or in a week, in 

 104 cases, that is in 

 fifty per cent., the 

 plants had dry inde- 

 hiscent fruits ; whilst 

 in seventy instances, or 

 thirty-three per cent., 

 the plants had small 

 seeds, such as we find 

 in the cruciferae, cary- 

 ophyllaceas, and jun- 

 caceae. Plants with 

 large seeds, such as 

 Convolvulus arvensis and 

 Nnphar luteum, made 

 up seven per cent, 

 of the total, the re- 

 maining ten per cent, 

 including plants with 

 berries and other mis- 

 cellaneous fruits. Of 

 the thirty-five species, 



where the period of flotation extended over six 

 months and considerably beyond, thirty species, or 

 eighty-five per cent., possessed dry indehiscent 

 fruits; the small-seeded plants with dehiscent 

 fruits not being represented, but only those with 

 large seeds such as Convolvulus septum and Iris 

 pscudaconis. 



In so far, then, as Nature has employed the 

 agency of water in the dispersion of our plants, 

 she has for the most part ignored the small seeds ; 

 and if she has availed herself of this agency at all 

 she has confined its operation almost entirely to 

 the dry indehiscent fruits. M. Kolpin Ravn has 



Corn Bluebottle. 

 Fig. 2 



recently been investigating the minute structure of 

 the coverings of such fruits with the object of 

 determining the causes of their flotation. (" Saertryk 

 af Botanisk Tidsskrift," ig Bind, 2 Hefte, Copen- 

 hagen, 1S94.) Aided by the previous labours of 

 others, he enables us to assign a function to certain 

 of their structural peculiarities. Meanwhile, 

 accepting the fact of their buoyancy, we will 

 endeavour, if possible, to ascertain if Nature has 

 made any very evident use of it. In the first place 

 we turn to the possible means of transportal by the 

 ocean currents. Except in the case of the littoral 

 plants, it is difficult to determine to what extent 

 our plants could have 

 been aided by this 

 mode of dispersal. 

 That this agency is 

 not essential is evi- 

 denced in the great 

 areas of distribution 

 belonging to such 

 plants as Prunella vul- 

 garis and Luzula cam- 

 pestris, where the fruits 

 or seeds have no float- 

 ing powers. Birds take 

 such an active part in 

 carrying seeds over the 

 globe that the inter- 

 vention of the ocean 

 current seems almost 

 superfluous. They 

 transport the seeds 

 from station to station, 

 and in this respect 

 alone possess a great 

 advantage over the 

 currents as seed -dis- 

 tributors ; and in many 

 other ways the cur- 

 rent as an agent in 

 distributing plants is 

 inferior to the bird. 



It is possible, how- 

 ever, that the effects 

 of buoyancy in dry 

 show themselves more 

 I have arranged in two 

 groups the species with fruits of this character. 

 The first group contains fifty-two species that 

 live at the edges of rivers and ponds, and of 

 these more than half possess fruits that are 

 able to float for a long time, usually for several 

 months. The second group contains seventy-one 

 species, frequenting drier situations, and here only- 

 five species possess fruits with any floating powers. 

 Some typical examples of these groups will be 

 given in next number. 



6, Fairfield West, Kingslon-oii-Thames ; February, isyj. 



yantis. Mons. 



indehiscent fruits may 

 clearly in other ways. 



