EMBRYO 



The fertilized egg divides transversely, producing al arge lower 

 cell and small upper cell, x^s in Naias (Campbell, 1897, p. 26), 

 Zannichellia (CampbeU, I.e., pp.27, 28), Zostera (Rosenberg, 1901, I; 

 Hofmeister, 1852), and Potamogeton (Wiegand, 1900), the former 

 divides no further, but subsequently increases vastly in size, develop- 

 ing large vacuoles, and becomes the suspensor, which is thus in 

 this case restricted to a single large, basal cell. 



I was unable to discover any stages between the two-celled pro- 

 embryo and the twelve-celled stage — the latter represented in 

 PL XIII, fig. 100. Murbeck, however, figures a three-ceUed stage 

 in Ruppia rostellata, which 1 reproduce (PI. XIII, fig. 98), showing 

 two small cells, which may be called the " embryo-ceUs," arisen from 

 the transverse division of the small upper cell ; and also the basal 

 large ceU, namely, the suspensor-cell. Wille (1883) figures and 

 also describes a similar stage in his work on the embryo of Ruppia 

 rostellata. 



Wille has carefuUy followed the development of the proembr}'© 

 in these early stages, and his observations and figures accord well 

 with my slightly older embryos. His report of the succeeding 

 divisions is briefly as follows : The lower of the two embryo-cells 

 divides longitudinally, followed by a similar division in the same 

 plane in the upper cell, making four cells in all ; next, by longitudinal 

 divisions in both segments, in a plane at right angles to the last, 

 an eight-celled structure is formed. The embryo now consists, 

 therefore, of two four-celled segments lying one over the other, 

 and borne on a single large suspensor-cell (PL XIII, fig. 99.) 



It should be borne in mind that this suspensor cell is the basal 

 segment resulting from the first division of the fertilized egg, and 

 never again divides. In this connection it may be well to follow 

 out the subsequent history of this peculiar suspensor before going 

 into an account of the embryo proper. 



After the first unequal division in the fertilized egg-cell, the 

 suspensor-ceU becomes rapidly larger, and at the time when the 

 two four-celled segments appear, as described above, it is much 

 larger than these combined (PL XIII, fig. 99). At the period shown 

 in Fig. 100, when the embryo contains twelve cells, the suspensor- 



