34^ CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



always divide before quadrants are formed in the first seg- 

 ment. Quadrants are formed in segment I first, but there 

 is no regularity in the quadrant divisions of the other pri- 

 mary segments. In some embryos quadrants are formed with 

 regularity in all the primary divisions of the embryo, begin- 

 ning with the distal primary segment ; but in others, as in the 

 embryo from which figure 35 was drawn, segment III has 

 divided only once, although quadrants had been formed in 

 the second segment, and in the first, octants. Segments I 

 and II show greater regularity in cell formation than the 

 third segment in the early as well as in the later stages in 

 the growth of the embryo. 



Octants are formed in the distal segment by anticlinal 

 walls which strike the quadrants at an acute angle, gener- 

 ally below the middle, and not as stated by Norner, at right 

 angles to them. Of the octants thus formed the four upper- 

 most form part of the dermatogen and divide subsequently 

 by anticlinal walls only. The octants are usually formed as 

 figure 35 indicates, while segment II is yet in the quad- 

 rant stage. This is, however, not at all uniform, and peri- 

 clinal walls are sometimes met in the second segment 

 before the octants are completely formed (fig. 36). 



As just stated, the first periclinal divisions occur in the 

 second segment. These are followed by similar division 

 walls in the end segment. Segment III, in which the divi- 

 sions are very irregular, does not take part in the periclinal 

 divisions above mentioned. The plerome is cut off as in 

 Lilcea (Campbell, 1898) in the two end segments at about 

 the same time. This was found also in the grasses by 

 Norner (1. c). In some cases in Avena it occurs, at least, 

 in the end segment first (fig. 38). 



An examination of the cells of the young embryo shows 

 an increase in number and size of the vacuoles in the micro- 

 pylar end. This peculiarity, together with the irregularity 

 of cell divisions, serves in a way to mark the descendants of 

 the third segment. 



The suspensor, which is formed when segment III is cut 

 off, remains small, does not divide, and plays an incon- 

 spicuous part in the history of the embryo. A large vacuole 



I 



