30 DOUGLAS HOUGHTON CAMPBELL ON THE 



proceeds ouhvard. The tracheids are all short and pointed, forming a cylinder which 

 constitutes the greater part of the bundle. They are marked with transversely elon- 

 gated pits, or with shorter ones placed in two or three rows. The remainder of the 

 bundle consists of one or two layers of narrow cells surrounding the tracheary tissue, 

 their cells having more or less oblique transverse septa. The ground tissue of the root 

 consists of about four layers of large parenchymatous cells, about three times longer 

 than broad. In those nearest the base of the root, chlorophyll is present, but it is wanting 

 in the subterranean parts. The cells of the outer layer differ but little in form from 

 those of the ground tissue, except in being narrower, but their walls soon become brown 

 and thickened, and, finally, the contents disappear, leaving them dry and scaly. From 

 the outer surface of the cells abundant root-hairs are formed. 



The second root, like all the subsequent ones, is endogenous in its formation. The 

 apical cell is formed in the tissue at the base of the second frond near the point at which 

 the bundle of the leaf connects with that of the stem. As the root grows, its central 

 cells become divided by longitudinal walls into a cylindrical mass of cells, the procam- 

 bium of its fibro-vascular bundles, its growth beginning with the cells that lie in contact 

 with the bundle of the stem. The formation of the second root begins while the second 

 frond is still young and before it is unrolled. The root breaks through the base of the 

 leaf about the time that the frond unrolls. The tip of the root contains enough chloro- 

 phyll in very fine granules to give it a decided green coloi" this, however, not extending 

 for any great distance, the cells nearer the base being nearly colorless. The first devel- 

 opment of permanent tissue in the bundle takes place at two points instead 'of one. Two 

 rows of narrow spiral tracheids are formed simultaneously near the foci of the ellipti- 

 cal bundle, and the development of the tracheary tissue proceeds inward. The rest of 

 the bundle is composed of narrow elements similar to the corresponding tissue of the first 

 root. 



The bundle of the young stem is solid instead of being a hollow cylinder as in the 

 mature plant. This is partly composed of scalariform tracheids Avhich are short and 

 pointed and rather broad. There are also spiral and reticnlate ones, especially in the 

 center of the bundle. The bundle anastomoses with the base of that of the first frond, 

 the traclieary tissue of the two bundles being in contact. The bundle runs toward the 

 second leaf into which it sends a branch, but tracheary tissue is developed in the stem- 

 bundle beyond the point of contact of the two bundles before any tracheary tissue is de- 

 veloped in the bundles of the leaf. As in the ease of the other bundles, no other tissue 

 than the tracheary is completely differentiated. 



The procambium of the stem-bundle can be traced nearly to the apex of the conical 

 growing point which soon becomes so covered with the broad scales that it is often dif- 

 ficult to get at it. 



The young plant grows rapidly. By the time that the third or fourth leaf is fully de- 

 veloped, the stem has assumed some size and the bundle running through it has become 

 sharply differentiated by the formation of a bundle-sheath Avhose cells assume a brown 

 color. 'New roots continue to form endogenously from the bases of the young fronds, 

 the formation beginning before the leaf is fully grown. 



The new leaves arise from segments of the apical cell of the stem, and up to the fifth 



