W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTERA. 253 



inner and two outer in the fourth cell, the final result, under 

 either hypothesis, would be the formation of a central (apical) 

 cell surrounded by a chaplet of eight cells. 



During the transformation of the smaller segment of the im- 

 pregnated germinal vesicle into a globular cellular body, the 

 enveloping membrane of the nucleus, which has become a tough 

 coat of the embryo-sac, adheres most intimately to the inside of 

 the inner integument. The edges of contact of the cells of the 

 latter soon make marks upon the hitherto homogeneous, smooth 

 membrane in the form of cellulose ridges running upon it ; at 

 first extremely delicate, scarcely perceptible, but gradually more 

 distinct, and at last so sharp, that the wall of the embryo-sac 

 most deceptively resembles, when seen only on the surface, a 

 layer of tubular cells filled with transparent contents. The pe- 

 culiar conditions of this enveloping membrane, its lengthened 

 vital activity, its energetic growth, and its nutrition by the 

 tissues and cells of different kinds which it encloses, deserve 

 particular attention. 



From one of the broad surfaces of the laterally-compressed, 

 ovate rudiment of the embryo springs an obtusely conical pro- 

 jection of cellular tissue, the rudiment of the future principal 

 axis of Zosiera, which is thus a secondary axis, a lateral sprout 

 of the leafless axis of the first rank, of the embryo. Very soon 

 after the appearance of the new structure, the first leaf is deve- 

 loped, a little below its apex (figs. 30, 31, 33-35). This presents 

 itself as a little ridge nearly surrounding the end of the stem, 

 and very rapidly grows higher at the border turned to the cha- 

 laza, than at other parts. The leaf grows longitudinally through 

 constant repetition of the division of a transverse row of apical 

 cells, by walls inclined alternately towards the upper and lower 

 surfaces of the leaf, and by division of the cells of the second 

 degree by cross walls. The direction of its growth is parallel to 

 the primary axis of the embryo, diverging at right angles from 

 its parent axis. 



During the development of this leaf, a very considerable alter- 

 ation occurs in the shape of that axis of the first rank : by active 

 multiplication of its cells, predominantly in the directions of 

 breadth and length, the ellipsoidal cellular body becomes a flat 

 mass truncated below and gradually attenuated toward the upper 



