ANGIOSPERMS. 



399 



which appear in basipetal succession, while longitudinal walls are formed at the same 

 time in the terminal cell, and with the result, as in Capsella, that two walls are formed 

 at right angles to one another. But in this case the chief portion of the embryo does 

 not proceed solely from the terminal cell of the pro-embryo, but the other cells m and n 

 also take part in its formation, as appears from Fig. 330 III. The separation of the 

 dermatogen by periclinal walls takes place later in Alisma than in Capsella, but the 



i 



FIG. 329. Extremity of the root of an embryo 

 of a Dicotyledon ; i and 2 the first layers of the root- 

 cap, d dermatogen, / periblem, // plerome. After 

 Hanstein. 



FIG. 330. Embryogeny in Alisma Plantago. I pro-embryo, consisting of three cells. The cell q subsequently 

 swells into a spherical shape, the cotyledon springs from / and portions of the embryo and suspensor from r ; four cells 

 are formed by three transverse walls in basipetal succession from the middle cell r in No. //, ?, n, o,p; from m the 

 plumule is developed, n gives rise to the greater part of the radicle, o and / to the hypophysis. /// upper part of an older 

 embryo, in which the dermatogen has been formed by periclinal walls ; / denotes those cells which proceeded from the 

 terminal cell / of the preceding figure. IV optical transverse section of the same embryo. V an older embryo, in which 

 the rudiment of the plumule may be seen on the side to the right, where are the larger cells of the dermatogen. tThe 

 letters indicating the groups of cells also indicate the cells from which they are formed (see also Fig. 332). After Famintzin. 



layers which produce the periblem and plerome are as distinctly marked off from the 

 first, according to Famintzin, in the one case as in the other. But the origin of the 

 organs is different in the two embryos. In Alisma the whole of the terminal mass of 

 tissue occupying the apex of the embryo becomes the cotyledon, which is therefore 

 terminal on the embryo, while the growing point of the stem is placed laterally upon 

 it, where a slight depression appears on the right side of V in Fig. 330. This 

 separation may be traced back to the first cell-divisions. The cotyledon is produced 

 from the terminal cell / and from the cells formed by its division, the cell next below m 

 forms the middle portion, which is distinctly marked off from the cotyledon and from 

 the radicle and gives rise to the plumule, and the third cell n becomes the radicle ; 

 o and/ form the hypophysis, and p therefore a part also of the embryo. Fig. 332 

 shows that the termination of the radicle proceeds from the hypophysis in the same 

 way as in Capsella. 



The two examples which have been now briefly described do not however at all 

 supply schemes of development of the embryo that are generally applicable to 

 Monocotyledons and Dicotyledons. Other forms that have been examined show 

 variations in almost all the processes of differentiation observed in Capsella and Alisma. 

 As regards the position and origin of the organs, the important point of difference 

 between Monocotyledons and Dicotyledons has been already noted, that in the 



