296 F. O. BOWER. 



throughout the vascular Cryptogams, of constant orientation 

 relatively to the other members of the embryo. 



Turning now to the Angiosperms, it has been shown by 

 Tscherning/ Flahault," Darwin/ Briosi,^ &c., that in various 

 plants belonging to different natural orders outgrowths of 

 the peripheral tissues of the hypocotyledonary axis occur in 

 the young seedlings. These outgrowths assume very different 

 forms ; their position is at the point of transition from stem 

 to root ; in most cases they are formed shortly after germina- 

 tion begins. In function these heels or pegs, as they have 

 been called, differ from the organs which we have been con- 

 sidering. They have in no case been described as effecting 

 a transfer of stored-up nutritive materials to the young seed- 

 ling; their functions are chiefly mechanical. Looking at 

 them from the point of view of structure, however, they 

 coincide Avith the organs above considered, since they are 

 formed by lateral extension of the tissues of the hypocotyle- 

 donary axis. The tissues outside the vascular bundles are 

 chiefly concerned in their formation. These heels or pegs 

 are found only in a comparatively small number of seedlings 

 of the Angiosperms. It has already been observed that such 

 outgrowths are not of universal occurrence in the vascular 

 Cryptogams and Gymnosperms. 



DraM'ing together the results hitherto obtained, we see 

 that in a large number of vascular plants, from the Ferns 

 upwards, the tissues of the hypocotyledonary axis are capable 

 of a lateral extension, accompanied by division of the cells ; 

 that the outgrowths thus formed are usually seated at or 

 near to the point of transition from stem to root ; further, 

 that the orientation of such structures is not uniform in all 

 cases, nor, indeed, in some cases, even in the single indi- 

 vidual [e.g. Gnetum, Vv^elwitschia, Cucumis). Lastly, that, 

 as we rise in the scale of development, the time of first 

 appearance of the outgrowth is later, and may be seen to 

 correspond to the time at which it will be required to per- 

 form its functions. The inconstancy of occurrence, orienta- 

 tion, and time of first appearance of these outgrowths seems 

 to point to the conclusion that they are not to be regarded 

 as clearly-defined morphological members, but rather as 

 swellings of the tissue of the hypocotyledonary axis, which 



' 'Uuters. liber die Eutwickelung einiger Embryoueu.' Inaug. Diss. 

 Tubingen, 1872. 



* 'Eulletiu Soc. J3ot. de France,' vol. xxiv, p. 201. 1877. 



2 ' Tiie Movements of Plants,' p. 102. 1880. 



^ ' Sopra uu Organo Pinora uon avvcrtito di alcuni Embryoni Vegetali.' 

 Roma, 1882. Cf. also ' Bot. Zeit.,' p. 311. 1882. 



