216 Cook : Potamogeton lucens 



The number of cells in acropetal succession may be six in 

 number. When three cells are formed the apical cell divides by 

 the formation of two longitudinal walls at right angles {figure 15) 

 and this is followed by cross and longitudinal divisions of the sec- 

 ond and third cells {figures 16, iy y /<?, 20, 21). Thus far the 

 formation of the embryo is in harmony with the descriptions given 

 by Wiegand and Holferty for I\foliosus and . 



The further development of the embryo shows some variations 

 at this point, in some cases showing three well-defined segments 

 {figures 18 \ ip, 2i), while in others it showed only two, as indi- 

 cated in figure 20. The writer is unable to say positively whether 

 the formation of the parts is strictly in accordance with the Alisma 

 type or whether there is a variation as described by Campbell (1) 

 for Zannichellia, but is inclined to the former view, which is assumed 



to be true in the further discussion of this subject. It will be 

 noted at this time that figure 20 corresponds quite well to Wie- 

 gand's figure 26. 



The apical cell, as previously stated, divides and eventually 

 gives rise to the cotyledon. The second cell divides by a cross- 

 wall ; of these two daughter-cells the one next to the apical cell 

 divides, forming a second segment from which is derived the apex 

 of the stem. The other daughter-cell forms the third segment 

 and part of the suspensor by which the embryo is attached to 

 the large basal cell. From this third segment are derived the 



hypocotyl and the root-tip. These three segments are shown in 

 figures 18, ig t and 21. Cell a of figures 18, 20, and 21 divides 

 transversely into cells a and a! of figure 22. Cell a of figure 22 

 evidently forms in part or entirely the dermatogen of the root-tip 

 {figures 2j f 24), while a' of figure 22 divides to form cells a f and 

 a" of figure 2j. Cell a' of figure 23 now undergoes division to 



A 



a part of the suspensor. Shortly after this, the plerome and 

 periblem show indications of differentiation {figure 24). 



As previously stated, with the appearance of the cotyledon 

 (figure 23) the large vesicular basal cell of the suspensor shows 

 signs of disintegration. The suspensor is always delicate and the 

 embryo even in its early stages is frequently found separated from 

 the basal cell. 











