Bibliographical Notices. 



409 



laria the protruded end of the embryo developes into an upright 

 green filament (jprimary leaf, cotyledon), at the base of which a 

 bud, already formed, produces a stem with long filiform leaves. 

 The opposite end of the embryo becomes a root and breaks 

 through, somewhat later, the green mammilla nuclei of the ovule, 

 which here also appears as a sheath. 



Pilularia globulifera. A, Transverse section of an ovule at the com- 

 mencement of development ; a, gelatinous envelope ; 6, coriaceous coat ; 

 c, embryo-sac filled with starch and drops of oil ; d, mammilla of the nucleus. 

 B, Pollen grains ; a, fresh from the pollen sac ; b, swollen in water and at 

 the commencement of the formation of the tube. C, Upper part of the 

 ovule after the penetration of the pollen tube d; a, coriaceous coat; 6, em- 

 bryo-sac ; c, nucleus and its mammilla ; k, layer of cells which separate the 

 pollen tube from the embryo-sac. E, Pollen tube from C prepared free; above 

 it shows the still uncovered portion which was inclosed in the outer pollen 

 membrane, in the middle the more slender special tube, and below the broad 

 expanded part already filled with cellular tissue, which developes into the 

 embryo. D, Upper end of the ovule in a further advanced stage of de- 

 velopment ; a, coriaceous coat ; b, embryo-sac ; c, nucleus and its mammilla, 

 expanded by the development of the embryo into a sac ; d, stem-end of the 

 embryo (e); g, primary leaf (cotyledon) ; h, pollen tube ; /, first axillary bud ; 

 i, capillary, outstretched external cells of the nucleus; k, layer of cells 

 which separates the embryo from the embryo-sac. 



BIBLIOGRAPHICAL NOTICES. 



The Physical Atlas ; a series of Maps illustrating the Geographical 

 distribution of Natural Phenomena. By H. Berghaus, LL.D., 

 F.R.G.S. &c, and A. K. Johnston, F.R.G.S. &c. 



It is with no small pleasure that we find ourselves called upon to 

 notice this important undertaking, especially in the improved form 

 under which it is here presented to the British world ; the compre- 

 hensiveness of the design and the care which is bestowed upon its 

 Ann. $ Mag. N. Hist. Vol. xviii. 2 G 



