. The Eusporangiatae; the comparative morphology of the Ophioglossaceae and Marattiaceae. Ophioglossaceae; Marattiaceae. THE YOUNG SPOROPHYTE 63 make a nearly continuous crescent-shaped mass of procambium. Fig. 44, A, B, shows the section of the central stele; and the space between the horns of the crescent, i. e., the space between the third and fifth leaf traces, constitutes the so-called "foliar gap" which faces the second leaf trace. The central cells of the young stele have already begun to form cambium, which in the older stem constitutes such a char- acteristic feature of the
. The Eusporangiatae; the comparative morphology of the Ophioglossaceae and Marattiaceae. Ophioglossaceae; Marattiaceae. THE YOUNG SPOROPHYTE 63 make a nearly continuous crescent-shaped mass of procambium. Fig. 44, A, B, shows the section of the central stele; and the space between the horns of the crescent, i. e., the space between the third and fifth leaf traces, constitutes the so-called "foliar gap" which faces the second leaf trace. The central cells of the young stele have already begun to form cambium, which in the older stem constitutes such a char- acteristic feature of the stele. Before any tracheary tissue is formed in the young stele, a few thick-walled cells can be seen in the outer part of the portion of the stele corresponding to the third leaf trace. These are protophloem cells, and similar ones are developed later in the younger parts of the stele. The first tracheary tissue appears in the region of the steel section belonging to the third leaf trace. In the section shown (fig. 44, C). Fig. 44. ABC Theyoungvascularbundlesof sections E,F,G, of the series shown in fig. 43. X150. D. Section of a young sporophyte of Botrychium virglnimum, showing junction of a leaf trace with stele of axis. X75. there are three groups of these primary tracheids, separated by a considerable interval and placed at the extreme inner limit of the young stele. In the older portions of the bundle the number of these increases and similar ones make their appearance in the next younger section of the stele, that belonging to the fourth leaf. Last of all these primary tracheids are formed in the younger region of the stele and new ones arise between these first-formed ones, so that there is developed a nearly complete circle of tracheids marking the inner boundary of the tubular stele. The second leaf trace approaches nearer and nearer the two horns of the crescentic stele section as it is followed downward, and finally joins it, filling up the gap between the regions
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
