190 MORPHOLOGY OF ANGIOSPERMS 



possible to correct some inaccuracies, and at the same time to 

 show that the early divisions of the fertilized egg do not follow 

 such a definite sequence as had been supposed. The following 

 description is based upon his account. The fertilized egg di- 

 vides by a transverse wall, and the resulting basal cell becomes 

 large and vesicular, but does not divide. The apical cell divides 

 by a transverse wall and a prpembryo of three cells is the result 

 (Fig. 82). The terminal cell (Fig. 82, c) gives rise to the ter- 

 minal cotyledon, and its first division, which may take place im- 

 mediately or may be somewhat delayed, is always longitudinal. 

 From the middle cell there are developed the lateral stem-tip, 

 the root-tip, the hypocotyl, and all of the suspensor except the 

 vesicular basal cell. The middle cell divides transversely, and 

 of the two resulting cells the one next the- terminal cell gives rise 

 to the stem-tip (Fig. 82, C', s). In general, the ^differentiation 

 is basipetal, proceeding from the cotyledon toward the suspen- 

 sor. The terminal or cotyledon cell having divided by a longi- 

 tudinal wall, the next division is transverse, resulting in the 

 quadrant stage, followed by the octant stage. At this stage 

 the dermatogen begins to be differentiated, appearing first in 

 the cotyledon and proceeding toward the root end of the em- 

 bryo. While the cell from which the stem-tip arises can be 

 identified in the four-celled proembryo, it is only in much later 

 stages (as Fig. 82, 7) that it is readily recognized. In the 

 four-celled proembryo (Fig. 82, (7) the cell next the vesicular 

 cell divides transversely ; and of the two resulting cells the one 

 nearest the vesicular cell by one or more transverse divisions 

 gives rise to a filamentous suspensor of two to six cells; from 

 the other cell are developed the root and the hypocotyl. The 

 dermatogen is usually developed, even around the root-tip, be- 

 fore any differentiation of periblem and plerome can be dis- 

 tinguished (Fig. 83). 



This Alisma type has proved to be characteristic, not of 

 Monocotyledons in general, but of the more primitive hydro- 

 phytic forms. Its main features are an undividing and usually 

 much enlarged and swollen basal cell cut off by the first division 

 of the fertilized egg, and a proembryo of three cells whose mid- 

 dle cell divides basipetally to form the region of the embryo 

 behind the cotyledon, and also forms more or less of a suspensor 

 in addition to the large basal cell. As further illustrations of 



