W. HOFMEISTBR ON THE DEVELOPMENT OP ZOSTERA. 241 



Zostera marina, to a series of twelve, in Zostera minor only of 

 six ranks. 



The rudiments of the first spadix of Zostera marina appear at 

 the beginning of spring, those of Zostera minor in the middle 

 of summer. From then until the period of maturation of the 

 first seeds (in Z. marina at the beginning of July, in Z. minor 

 the beginning of September), new flowering sprouts arise suc- 

 cessively in the axils of the bracts {vorblatter) of their predeces- 

 sors, so that, from the middle of May forwards, every fertile 

 plant of the common Zostera exhibits a series of distantly situated 

 stages of development of the floral organs*. 



When arising out of the axil of the sheathing leaf Of the pre- 

 ceding sprout, the axis of a new rank, terminating in an inflores- 

 cence, presents itself as a hemispherical papilla (fig. 1 d), the 

 side of which facing the parent sprout coheres with the latter up 

 to the point where the new shoot forms its first, sheathing leaf, 

 by the simultaneous multiplication of a zone of cells situated 

 close underneath its apex. The multiplication of the cells of 

 both organs, axis as well as leaf, in the longitudinal direction, 

 commences with a repeated subdivision of their apical cells — in 

 the axis of a single one, in the leaf of an incomplete crown of 

 similar cells — by means of alternately obliquely inclined walls. 



The fertile shoot forms its single stem- leaf [laub-blatt), oppo- 

 site to the leaf-sheath, shortly aft;er the latter breaks forth. The 

 bud of the sprout of the succeeding rank appears simultaneously 

 in the axil of the basilar sheath. 



The stem-leaf {laub-blatt) makes its appearance as a flat 

 cellular mass embracing the end of the stem so completely as to 

 leave only a narrow slit. It first grows longitudinally, by re- 



* The interpretation of the series of sprouts of the flowering Zostera given 

 above, placed beyond doubt by investigation of the development, is also the only 

 one possible, looking exclusively at the condition when complete. Neither is 

 the supposition admissible that the flowering sprouts, upwards from the sheath- 

 ing leaf, are a series of equivalent secondary axes of a main axis bearing only 

 sheathing leaves, for the sheath is opposite to the sprout terminating as an in- 

 florescence ; — nor is that which would make the inflorescence an axillary bud of 

 the stem-leaf {laub-blatt) which sheathes the spadix with its base, for this as- 

 sumption would lead us to expect each couple of leaves of the main axis, a 

 stem-leaf (laub-blatf) and a leaf-sheath, to stand regularly one above the other; 

 a conception untenable when we recollect the ^ position of the leaves of the 

 sterile plant of Zostera. 



SCIEN. MEM. -^Nat. Hist. Vol. I. Part III. 16 



