Structure and Division of the Vcgctahle Cell. 197 



divides. Though, owing to its small size, I have only 

 once seen wluit appeared to be a median constriction, 

 there can be little doubt that this is the course of events, 

 for two distinct ones can often be discerned in cells about 

 this period. The nucleolus next elongates, and this almost 

 invariably parallel to the plane of the former cell-division. 

 Sometimes it may form an acute angle with it, or even may 

 elongate at right angles, the first, however, is by far the 

 commonest method. A constriction is then carried through 

 the centre of it, which deepens till complete separation into 

 two results, each carrying with it a nucleolo-nucleus (Plate 

 IX. figs. 1 and 2). That increase in its size goes on at this 

 time cannot be doubted, since the two new nucleoli are each 

 nearly of tlie same size as was the parent one at its initial 

 period of division. The nucleus next elongates slightly in 

 the same plane as did the nucleolus, the protoplasm 

 collects considerably around it ; next, by movement of what 

 seems the denser material of the nucleus towards the two 

 poles, a narrow but elongated clear sj)ace, traversed by very 

 delicate fibrils stretching from its two halves, appears running 

 at right angles to the plane of elongation of the nucleus, this 

 may be called the nuclear barrel. Shortly, in the middle 

 of it, there can be distinctly seen a double row of close- 

 set dots which, on focussing, seem to change their position, 

 almost giving one, at first glance, the idea of three parallel 

 rows. This results from different parts of the cell-plate 

 being seen as the focus is altered. Along this cell-plate 

 the new cellulose septum is deposited, and after a consider- 

 able interval it splits up to constitute the aperture of the 

 stoma. Even before the nuclear disc is visible the two 

 nucleoli take up positions on opposite sides of its area 

 (Plate IX. fig, 3). Such is the course of development as 

 far as I have been able to follow it. Strasburger gives 

 a very similar account, as far as nuclear division goes, of 

 the formation of a stoma in Iris ^mmila. In Oi'nithogahim, 

 however, elongation of the nucleus is not nearly so pro- 

 nounced as in it. 



We may seem now to have exhausted the complete 

 history of stoma development, but in many instances this 

 is not so. Even during the nuclear division one can often 

 observe that the nucleolo-nucleus of each half has again 



