THE EMBRYO 



137 



In my original study of Marattia I concluded that the primary divisions resulted 

 in the establishment of the organs of the young sporophyte in a manner similar to 

 that in the Leptosporangiatae, i. e., that the stem and leaf were derived from the 

 epibasal quadrant, the root and foot from the hypobasal ones. Farmer thought that 

 this was true for Angtopteris and Jonkmann assumes that it is the case also in 

 Marattia. A further study of my preparations, however, has led me to believe that 

 the whole of the hypobasal region is devoted to the foot, while the root, together with 

 the leaf and stem apex, are of epibasal origin. A large cell (fig. 106, A) occupies 

 approximately the same position as the stem apex in the older embryo and it is 

 possible that this may be the apical cell of the stem, but in the absence of the inter- 

 mediate stages this can not be positively asserted. For a long time the embryo 

 retains the oval form and there is scarcely any sign of the young organs of the 

 sporophyte which in the leptosporangiate ferns are so early manifest; indeed, 

 Jonkmann states that there is no differentiation at all, but a careful study of the 

 older embryo shows unmistakable indications of the definitive organs. The devel- 

 opment of the tissue in the epibasal region is not uniform, but somewhat to one 

 side of the center (fig. 106, B) there may be seen a group of columnar superficial 

 cells, which mark the position of the future growing point of the stem. Whether 

 one of these superficial cells is the 

 definitive apical cell it is impossible 

 to determine, but from a comparison 

 with the older stages, as well as with 

 corresponding stages of the embryo 

 in the other genera, it seems proba- 

 ble, at least, that this is the case, 

 and perhaps this initial cell may be 

 traced back to the centrally placed 

 cell noted in the younger embryo. A 

 considerable portion of the epibasal 

 tissue is not included in the meri- 

 stematic region, which is derived 

 mainly, at least, from only one of the 

 original epibasal quadrants. The 

 tissue adjacent to this meristematic region is made up of large cells with less dense 

 contents and smaller nuclei and differs in no way from the large cells of the foot, into 

 which this tissue insensibly merges and of which it may be said to constitute a part. 



In the embryo figured, it was not quite certain whether the root apex had 

 begun to form or not. It seems probable that the cell r is really the apical cell 

 of the young root, but except for its position it was not noticeably different from the 

 cells adjacent; however, as in Angioptnis and Darura there is no question that the 

 root originates in this position, it is probable that this cell is really the initial tor the 

 young root and is cut out from the base of the epibasal tissue near its junction with 

 the foot. This marked endogenous formation of the root is very much like that in 

 the embryo of Ophioglossum moluccanum, but differs entirely from the superficial 

 origin of the apical cell of the root in the embryo of the Leptosporangiates. 



The stem apex in the older embryo is of very limited extent, consisting of only 

 a few cells, of which one, as we have said, is probably the definite apical cell, although 

 it must be said that this point is very difficult to decide, as all of tin central cells 

 of this apical group look a good deal alike, but a careful study of both transverse 

 and longitudinal sections seems to point to one of these as tin apical cell, which in 

 shape is a good deal like that in the stem apex of Ophioglossum. In longitudinal 



Fig. 107. 



Two cross-sections of an old embryo oi Marattia 



A passes through the stem apex, J/, and base ,>t COtyli don, 

 B passes through root apex, r. X200. 



