Box.— Vol. I.] CANNON— AVENA FATUA. 347 



appears early in that part of the suspensor which touches 

 the micropylar end of the embryo-sac. The protoplasm in 

 the distal end of this cell (i. e. of the suspensor cell) rounds 

 itself off, a membrane separates it from the large vacuole, 

 and thus the embryo is attached to the micropyle by the 

 proximal ends of the side walls of the old basal cell. The 

 dotted lines in figures 33 and 34 indicate this attachment. 

 The embryo remains connected with the micropyle in this 

 manner until about the time when the primary tissues are 

 differentiated, and then the attachment is broken and it lies 

 free in the embryo-sac. The suspensor cell persists to form 

 the end of the coleorhiza. It was not seen to divide, but it 

 is not unlikely that in old embryos it may undergo a few 

 irregular divisions. 



The behavior of the suspensor resembles that of Spar- 

 ganium (Campbell, 1899), but not of Lilcea (Campbell, 

 1898) and Alisma (Schaffner, 1896), in which the suspensor 

 becomes a large and important absorbent organ. The 

 degeneration of the suspensor of Avena is doubtless associ- 

 ated with the development of the endosperm cells, which 

 closely invest the embryo, as well as with the prominent 

 synergid^ which here, as in the wheat (Koernicke), serve 

 to nourish the embryo in its youngest stages. 



After the primary tissues are cut off, the embryo increases 

 in size, mainly in length, by growth which is almost wholly 

 confined to segments I and III. The embryo is club- 

 shaped, pointed at the micropylar and blunt at the distal 

 end. The periblem and plerome cells undergo few longi- 

 tudinal divisions, dividing mostly by transverse walls. This 

 makes the boundaries of the primitive segments difficult to 

 trace. Cross-sections through the middle of the embryo 

 show a plerome of about eight cells surrounded by a peri- 

 blem two or three cells thick. The two are very similar, 

 being composed of relatively large cells. The dermatogen 

 is made up of regular and comparatively small cells. A 

 cross-section near the micropylar end, through segment III, 

 shows a greater irregularity in the structure of the dermat- 

 ogen and internal tissues, which are not differentiated into 

 plerome and periblem. 



