242 W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTERA. 



peated subdivision of the cells of its upper border. The multi- 

 plication of these cells, on the side turned away from the slit, of 

 this organ (hitherto resembling a cylinder slit up lengthways), 

 soon outstrips that of the apical cells of the other half of the 

 leaf: the riband-shaped lamina grows out from the sheath. The 

 multiplication of the cells at the apex of the leaf ceases early, 

 while a very active and long persistent increase occurs in those 

 of the base. 



After the rudiment of the stem-leaf [laub-blatt) has been 

 formed, the end of the stem above it changes its form. It be- 

 comes widened out by a multiplication of its cells, predominantly 

 in the direction parallel to the surface of the leaf, and it assumes 

 the shape of a thick spatula, slightly concave at the side nearest 

 the next (younger) sprout. The rudiment of the flattened spadix 

 is now unmistakeable in the end of the axis. The longitudinal 

 growth of the spadix is continued by a frequently repeated divi- 

 sion of its apical cells by means of walls inclined alternately 

 towards the upper and lower surfaces of the leaf-hke organ. 

 The cells in the median line and at the margins of the spadix 

 remain long capable of multiplication; constituting strings of 

 cambium structure. On the other hand, two broad strips of 

 cellular tissue, parallel to the lateral borders of the spadix, early 

 cease to increase. With the exception of those composing the 

 epidermis, all these cells become separated from each other at 

 their angles; air becomes excreted in the intercellular spaces 

 (fig. 3). The cells of both the marginal strips of cambium on 

 the upper side of the spadix become greatly multiplied through 

 repeated division by walls parallel to its surface. In this way 

 are formed two swollen tracts of cellular tissue, which, in their 

 further development, become curved strongly inwards so as to 

 cover in a great part of the upper surface of the spadix, through 

 the resistance which the sheath of the stem-leaf {laub-blatt), 

 closely enveloping the inflorescence, opposes to the unfolding of 

 them. In Zostera minor little leaf-like structures arise upon the 

 spadix near the lateral margins of its upper face, and these lie over 

 the surface of the spadix like clamps or claws. Zostera marina 

 exhibits no trace of such organs. From the median streak of the 

 spadix, which becomes greatly expanded by the active multiplica- 

 tion of its cells, arise the anthers and ovaries, upon the upper face. 



