266 



A\D DEVELOPMENT 



the disc be elongated to form an ellipse, the periclines also become 

 ellipses, while the anticlines are converted into hyperbolas confocal 

 with the periclines. If it have the form of a parabola, the periclines 

 and anticlines form two systems of confocal parabolas intersecting at 



Fig. up. Geometrical relations of cleavage-planes in growing plant-tissues. [From SACHS, 

 after various authors.] 



A. Flat ellipsoidal germ-disc of Melobesia (Rosanoff) ; nearly typical relation of elliptic 

 periclines and hyperbolic anticlines. B. C. Apical view of terminal knob on epidermal hair of 

 Pinguicola. B. shows the ellipsoid type, C. the circular (spherical type), somewhat modified 

 (only anticlines present). D. Growing point of Salvinia (Pringsheim) ; typical ellipsoid type, 

 the single pericline is however incomplete. R. Growing point of Azolla (Strasburger) ; circular 

 or spheroidal type transitional to ellipsoidal. F. Root-cap of Equisetum (Nageli and Leitgeb) ; 

 modified circular type. G. Cross-section of leaf-vein, Trichomanes (Prantl) ; ellipsoidal type with 

 incomplete periclines. //. Embryo of Alisma ; typical ellipsoid type, pericline incomplete only 

 at lower side. /. Growing point of bud of the pine (Abies} ; typical paraboloid type, both anti- 

 clines and periclines having the form of parabolas (Sachs). 



right angles. All these schemes are, mutatis mutandis, directly con- 

 vertible into the corresponding solid forms in three dimensions. 



Sachs has shown in the most beautiful manner that all the above 

 ideal types are closely approximated in nature, and Rauber has applied 



