46 DOUGLAS HOUGHTON CAMPBELL ON THE 



botli in k'ligtli and breadth, reaoliing nearly their full size before they begin to show any 

 differentiation. The cells are filled with colorless protoplasm, almost destitute of gran- 

 nies, and with a large and distinct nucleus, especially in the outer ones. The procam- 

 Itinni cylinder is broader in one direction, so that the section is elliptical. The first 

 permanent tissue is formed near the foci of the elliptical bundle, there being formed 

 almost simultaneously at both foci a single row of narrow, spii-al tracheids. These are 

 long with pointed ends, fitting closely together. At first the spiral markings are very 

 fine and close, but with further growth they separate somewhat and also become thicker. 

 A long row of them is completed before any trace of other tracheary tissue is to be 

 found. jVi'ound these primary tracheids are next formed two or three rows of similar 

 ones, and from the formation of tracheary tissue proceeds toward the center of the 

 bundle. 



An examination of the tissues of the complete root shoAV that the tissues are less fully 

 developed than in the aerial parts of the plant or the rhizome. The outer cells are dry 

 and l)roken, and from them are seen growing the remains of numerous root-hairs, which, 

 except in the younger ])arts, ai-e also dr}^ and bro^\m. 



The lateral roots arise in strictly acropetal succession and are ai-i-anged in two rows 

 on op2:)osite sides of the larger roots. Their formation begins ])el()re the tissues of the 

 bundle of the main root are differentiated. Just before the primar}' tracheids ai-e formed 

 in the latter, the apical cell of the secondaiy root is formed from one of the cells of the 

 bundle-sheath. The exact method of the formation of the apical cell was not traced, 

 but it seemed to arise from the formation of three walls in one of the cells of the bundle- 

 sheath so placed, as to include, together with the outer Avail of the cell, a tetrahedral 

 cell. This at once begins to grow and divide in the same way as the apical cell of the 

 main root, and the young root breaks through the overlying tissues of the main root 

 about the time that the first scalariform tracheids of the latter are com])lete. Its tis- 

 sues develop in the same Avay as those of the main ]'oot,-and the tracheids in the lower 

 part are in direct contact with its primary tracheids. The major axis of the bundle of 

 the secondary root is at right angles to that of the main root. 



The bundles of the secondary are joined to that of the main root, the secondary i-oot 

 being at right angles to the latter, a line jDassing through the center of the bundle being- 

 coincident Avith the plane traversing the major axis of the main bundle. The bundle- 

 sheaths are continuous and the tracheary tissue of the base of the secondary root ends 

 abruptly against that of the main root, the tracheids of the former being smaller than 

 the adjacent ones of the main root, and bent and flattened at the points of contact. 

 Owing to the distortion of these basal tracheids, the bundle is larger at the base than 

 elsewhere. The other elements of the bundle are also bent so as to connect the corre- 

 sponding ])arts of the two bundles. The structure of the lateral roots is essentiallj" the 

 same as that of the main root, but the section of tlu' l)undle is more nearly circular. 



Section VII. The Sporangium. 



The development of the sporangium begins while the fertile frond is still small, and 

 in order to procure the youngest stages most satisfactorily, it is necessary to begin with 

 them when the fronds are just beginning to unroll. The margins of the pinnae are so 



