BOOKS AND CURRENT LITERATURE 



Buoyancy of Seeds. — R. Lloyd Praeger has published' an interesting 

 paper in which are summarized his own and others' observations on the 

 buoj'ancy of seeds of British plants. He has tested 786 species and 

 adds the results for 114 others taken from the writings of other students, 

 principally that of H. B. Guppy, so that data for 900 species of British 

 plants is available. 



The term seed is used in its original sense, i.e., for the natural unit of 

 dispersal. The results show that 85 % sink at once or within a week, 

 5 % float for from one to four weeks, 3.3 % float from one to six months, 

 1.9 % float from six to twelve months and 4.4 % float for over twelve 

 months. The more buoyant forms are as a rule inhabitants of stream- 

 banks and seashores: 25 are aquatics, 42 marsh plants, 5 bog plants, 

 17 maritime plants, while 7 owe their buoyancy to their fleshy fruits 

 having been dried before testing. The remaining 33 species are mostly 

 plants of a mesophile habitat. Considering them by families the author 

 finds that in certain families, e.g., Papaveraceae, Cruciferae, Caryophjd- 

 laceae, Geraniaceae, Leguminosae, Crassulaceae, Saxifragaceae, Primu- 

 laceae, Gentianaceae, Scrophulariaceae and Juncaceae true seeds are 

 generally the units of dispersal and these practically all lack buoyancJ^ 

 On the other hand the Ranunculaceae, Compositae, Orobanchaceae, 

 Orchidaceae, Cyperaceae and Gramineae are mostly buoyant and in 

 most cases their unit of dispersal is either a one-seeded indehiscent fruit 

 containing or retaining air, or a seed with a loose test enclosing air. 

 Other families such as the Rosaceae, Umbelliferae, Rubiaceae, I^ricaceae 

 Boraginaceae, Labiatae and Polygonaceae show a wide variability in 

 respect to buoyancy. 



The author's results confirm those of Guppy in showing that there 

 is a marked relation between buoyancy and a seaside or riverside habitat. 

 There is also shown to be considerable variability in the seeds of a single 

 species. Seeds from fleshy fruits are found to be in general lacking in 

 buoyancy and fruit-bearing branches whether fresh or dry add greatly 

 to the power of dispersal by water as Darwin long ago pointed out. 



1 Praeger, Scient. Proc. Royal Dublin Soc, vol. 14 (N. S.) No. 3, 1913. 



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