138 



I III MAK.VI HALES 



sections this is somewhat wedge-shaped, the narrow end turned outward and the 

 broad base below. In cross-section this cell is nearly square in shape (rig. 107, A,x) 

 and there may be seen a fairly regular series of four segments cut from the lateral 

 faces. From the broad truncate base of the cell, segments are also cut off which 

 contribute to the inner tissue of the stem.* 



Much the greater part of the epibasal meristem contributes to the cotyledon, 

 which is soon evident as a broadly conical protuberance, somewhat flattened on the 

 side adjacent to the stem apex and merging gradually on the outer side into the large- 

 celled tissue which adjoins the foot. To judge from the limited number of young 

 embryos which I could examine, it seems that the growth of the cotyledon is not due 

 to the activity of a single apical cell, but this point was somewhat uncertain. 



By the time that the cotyledon is established, growth has progressed in the young 

 root, which now is seen to have a conspicuous apical cell, which divides rapidly 

 so that the root quickly elongates in a direction opposite to that of the cotyledon 

 (tig. 108). The apical cell of the primary root in M. doiiglam is not triangular in 

 outline, but more or less quadrilateral, whether seen in longitudinal or cross 

 sections (fig. 107, B). In form and segmentation it perhaps more nearly resembles 

 that of Dancea than it does the tetrahedral apical cell which occurs in the young 



primary root oi'Angiopteris. 

 Active cell divisions take 

 place also in the tissue of 

 the foot, which completely 

 incloses the young root and 

 becomes practically merged 

 with it, so that it is quite 

 impossible to say, at the time 

 the root emerges, just how 

 much of the tissue of its 

 outer portion really belongs 

 to the root itself and how 

 much is derived from the 

 original tissue of the foot. 

 The latter is now no longer 

 recognizable as such, the 

 young sporophyte apparently at this time being composed almost entirely of the 

 cotyledon and the very huge root, with the stem apex, King near their junction. 

 From a comparison with younger stages, however, it is perfectly evident that the 



I 1 . 10S. 



V Section of an advanced embryo o\ Xtttratti 



■ ■m e "t cot) ledon. 

 If. The cot) ledon, more enlarged. 



jusi before 



larged 



region of the embryo at this time is composed mainlv of tissu 



belonging to the foot, which is, so to speak, perforated by the root in its downward 

 growth. 



The development of the vascular bundles at a very early period is first evident 

 in the cotyledon, which almost as soon as it can be recognized at all is seen to have 

 a strand of procambium extending below it. If this procambium strand is traced 

 <1<>\\ nward, it is seen to continue without interruption into the base of the root, exactly 

 as it does in Ophioglossum moluccanum. No trace of a procambial cylinder can be 

 found extending into the stem apex, which gives rise only to the parenchyma of the 

 central pith. This early development of the vascular bundles in the cotyledon and 

 ioor was correcdy observed bv Jonkmann and Farmer, both for Marattia and 



* In a very recent paper in the Botanical Gazette (Feb. 191 1), Miss Charles states that the apical cell of the 

 stem in Marattia alata is at first triangular in cross-section. In older sporophvtcs the single apical cell was replaced by 

 a group of initial cells. 



