268 Morphologie und Teratologie. — Physiologie. 



pollen-tubes. The stamens are detached chiefly when assimi- 

 lation is active and their Separation is facilitated by the for- 

 mation of gases in the tissues. There are two microsporangia 

 and the pollen-grains remain in tetrads as in some other aqua- 

 tics. The papillär surface of the cutinized exine serves to float 

 the microspores, which are heavier than water, by imprisoning 

 a film of air. The two generative cells are already formed 

 when the pollengrain is shed and they remain attached by their 

 attenuated tips. The female flower just reaches the surface of 

 the water by the active elongation of the supraovarial portion 

 of the flower and on account of its imperviousness to moisture 

 forms the apex of a shallow depression about 2 cm. in area, 

 into which the pollen-grains slip. Only those grains in the 

 tetrads germinate which are in actual contact with the stigma. 

 The ovule presents no special features. The embryosac has an 

 antipodal process. The polar nuclei do not fuse until after ferti- 

 lization, which is of the usual double type. Unsuccesful pollen- 

 tubes form large terminal dilatations in the cavity of the ovary, 

 which persist for a long time after fertilization, and show clearly 

 the presence of the two attenuated generative cells as well as 

 the tube-nucleus. The embryo presents no very striking fea- 

 tures and is characterized by the rudimentary primary root 

 often found in aquatics. E. C. Jeffrey. 



DANDENO, J. B, The Relation ofMassAction and Physi- 

 calAffinity toToxicity, withlncidentalDiscussion 

 as to how far Electrolytic Dissociation may be 

 Involved. (Am. Journal of Sei. Vol. XVII. p. 437—458. 

 June 1904.) 



Concludes that there is no support to the theory of electro- 

 lytic dissociation from the physiological side. As far as the 

 effects of Solutions on the radicle of certain plants is concerned, 

 finds that the quantity of Solution present has an important 

 bearing on its action, and that the rate of diffusion is of signi- 

 ficance. The mechanical effect of the walls of a glass vessel 

 and even the shape thereof is of effect, while by the presence 

 of pure sand the toxic action was reduced 32 times. The action 

 of the sohlte on the radicle is very probably a chemical one. 



H. M. Richards (New York). 



Darwin, Francis, Note on the Geotropism of grass- 

 halms. (New Phytologist. 1903.) 



If a grass-halm be fixed immovably in a horizontal posi- 

 tion, the lower half of the swollen node grows considerably, 

 demonstrating Noll's statement that geotropic curvature is due 

 rather to increased growth on the lower side than to inhibition 

 of growth on the upper. Considerable growth in the longitu- 

 dinal direction of such a node, leading to rupture of the pul- 

 vinus is figured by the author. E. Drabble (London). 



