THE EMBRYO 



47 



The first division wall, the basal wall, as in the other Eusporangiatae, is, usually 

 at least, transverse to the axis of the archegonium (fig. 28, A). Each of the cells thus 

 formed is next divided by a vertical wall, so that the embryo is divided into approxi- 

 mately equal quadrants. Jeffrey states that the quadrants are next divided by a 

 third (transverse) wall, so that there is a regular octant formation (Jeffrey 1, page 

 16), but adds that this segmentation presents various irregularities and this is 

 confirmed by my own studies of the young em- 

 bryo. In B. lunarta, according to Bruchmann, 

 the octant divisions are very regular. 



In B. virginianum the young embryo is 

 often somewhat pointed above, and transverse 

 divisions of such embryos may show that the 

 octant formation is suppressed in the epibasal 

 region, and this tapering upper part of the young 

 embryo suggests a suspensor similar to that de- 

 veloped in Danaa, but less clearly defined, and 

 probably not determined by the first division of 

 the embryo. Whether the suspensor found by 

 Lyon in B. ohltquum (Lyon 1) originates in a 

 similar fashion remains to be seen. This elonga- 

 tion of the upper part of the embryo, whether it 

 is considered as a suspensor or not, is doubtless, as Jeffrey has suggested, useful 

 in pushing the developing embryo deeper down into the prothallial tissue. 



For some time, only anticlinal walls are formed, this showing especially plainly 

 in transverse section (fig. 31). Sooner or later periclinal walls are also formed, and 

 it is possible that in some cases the first periclinal wall in one of the large epibasal 

 cells may establish the initial cell of the root, but this is hard to decide. The early 

 stages of the embryo are extremely difficult to embed without shrinkage, and this, 

 together with the difficulty of securing a sufficient number of the right stages and 

 the impossibility of regulating the direction in which they are cut, makes the deter- 

 mination of the origin of the primary organs of the young embryo a peculiarly 

 difficult problem. 



Fig. 30. — Three longitudinal sections of a young 

 embryo of Botrychium virginianum. r, the 

 root; /, the foot. X200. 



Fig. 31.— Four horizontal sections of a young embryo of B . virginianum. 

 I is next the archegonium; i and 3 are nearly median sections. ^ 



Neither Jeffrey nor Bruchmann was able to recognize a root initial until the 

 embryo had attained a large size, and its origin could not be determined. In the 

 embryo shown in fig. 30, I am inclined to believe that the cell r is really the root 

 initial. Unfortunately, stages between this and the one shown in fig. 32, where the 

 root initial is unmistakable, were wanting, but the position and state of develop- 

 ment of the root in the latter harmonize with this supposition. My fig. 32 is evi- 

 dently of about the same size as Jeffrey's fig. 46, and probably an examination of 

 other sections of the series from which Jeffrey's figure was drawn would show the 

 root initial, as well as traces of the stem apex and cotyledon. 



