W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTERA. 247 



up into an obtusely conical hollow mass of cells perforated at 

 the apex (fig. 17). The ovule unfolds itself within the bulging 

 portion of the cavity, becoming curved downward. Simultane- 

 ously with the sudden commencement of the very considerable 

 elongation of the perforated mouth of the young ovary, to form 

 the canal of the style, begins the formation of the two integuments 

 (fig. 18). They arise close beneath the summit of the young 

 ovule, by a pretty nearly simultaneous commencement of rapid 

 multiplication in two zones of cells ; the development of the outer 

 coat of the ovule begins immediately after the inner coat becomes 

 visible. The lower part of the ovule, at this epoch by far the 

 larger, remains uncovered by the integuments. 



Both integuments grow longitudinally by constantly repeated 

 division of the crowns of cells at their summits, by walls alter- 

 nately inclined to and from the nucleus (fig. 19). The outer 

 integument soon acquires considerable thickness through two or 

 three repetitions of the division of the cells of the second degree, by 

 means of walls parallel to the free outer surface ; when the ovule 

 is fully developed, this coat is composed of lax tissue, traversed 

 by intercellular spaces full of air, enclosed by an epithelium 

 formed of cells one-fourth the size and filled with watery fluid. 

 The cells of the second degree of the inner integument, do not 

 become multiplied in the direction of the breadth until this coat 

 has grown up beyond the summit of the nucleus. Then, how- 

 ever, its upper margin rapidly becomes broader and thicker 

 through repeated division of the cells by means of walls parallel 

 to the long axis of the ovule ; the mouth closes in, leaving only 

 the narrow canal of the micropyle (PL VII. fig. 22) formed solely 

 by the inner integument ; the outer coat of the ovule, which comes 

 to a standstill when the inner begins to increase in size, becomes 

 grown over by the thickened margin of the micropyle. 



At the epoch when the integuments reach the level of the 

 summit of the nucleus, the latter is composed of an axial row 

 consisting of a few, eight to ten cells, enclosed by a double layer 

 of cells. A simple layer of cells covers the upper extremity of 

 the axial string and forms the summit of the nucleus (fig. 19). 

 As in most young organs of vegetables, the cells forming the 

 free outer wall of its surface possess tolerable firmness, different 

 from the gelatinous consistence of the cell-walls in the interior. 



