3IO CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



segments, instead of the three or four found in S. ramosum. 

 The small basal segment, which is in contact with the apex 

 of the embryo-sac, varies a good deal in size, this being 

 correlated with the form of the original embryo-cell. If 

 this tapers much, so as to have a small point of attachment, 

 the basal segment remains very small and pointed (fig. 42), 

 but if the embryo-cell is flattened where it is in contact 

 with the wall of the embryo-sac, the basal segment of 

 the embryo is correspondingly broader and shows more 

 divisions. 



A median section of such an embryo shows the limits of 

 the three primary segments still visible (fig. 38). This ter- 

 minal segment is very much larger than the others, and, as 

 already stated, relatively larger than in S . ramosum. The 

 first divisions in all the segments are median vertical ones, 

 and it is clear from studies of transverse sections that there 

 are normally intersecting median walls which divide each 

 segment into four equal quadrants. The divisions are less 

 constant in the basal segment, especially when it is small, 

 and transverse sections of this often show only two or three 

 cells, one or both of the second median walls being sup- 

 pressed. The next divisions are usually vertical also, but 

 there is evidently no absolute rule as to their arrangement. 

 In fig. 40 is shown a series of cross-sections of a young 

 embryo, and it is clear that the divisions are not always 

 entirely alike in the different quadrants of the same section 

 (see fig. 44, h^. Probably, in most cases, the first divi- 

 sion-wall formed in the quadrant is curved, and extends 

 from the quadrant-wall to the periphery. This is then fol- 

 lowed by a series of periclinals which cut off the epidermis. 

 Sometimes, however, it looks as if the first walls were peri- 

 clinals, thus determining at once the separation of the epi- 

 dermal layer. Hegelmaier shows much the same variation 

 in S. ramosum (e. g. his figures 6 and 8). 



The variations in the basal segment have already been 

 referred to. It may divide into equal quadrants (fig. 44, 

 a), but more commonly there is a suppression of one or 

 both of the second quadrant walls. Where the basal segment 



