THE YOUNG SPOROPHYTE 55 



III. THE YOUNG SPOROPHYTE. 



THE YOUNG SPOROPHYTE OF OPHIOGLOSSUM. 



As we have seen, the single vascular strand in the young sporophyte of Ophio- 

 glossum moluccanum is continuous through the cotyledon and root, and sections 

 at different heights show essentially the same structure throughout. The petiole 

 of the cotyledon (figure 27, A), which is traversed by two conspicuous lacunae, 

 shows that the axial bundle has a perfect collateral structure. The xylem consists 

 of a group of about a half dozen tracheids on the inner side of the bundle, of which 

 the endodermis, however, is not evident. If a section made in the mid-region of 

 the plant is examined, the only difference between its bundle and that within the 

 petiole of the leaf consists in the somewhat greater development of the tracheary 

 tissue. The section of the root bundle also almost exactly resembles that of the leaf. 

 Whether we call the root bundle monarch or collateral is merely a question of terms. 



r B 



Fig. 37. 



A-C. Three sections of a young sporophyte of Oplnovlo ; !um moluccanum with the first leaf, I 1 , of bud fullv 

 developed; r, primary root of sporophyte; r 1 , first root of bud; / 2 , second leaf of bud. 

 D. The stem-apex more highly magnified, showing the third leaf, / 3 . 



In the mid-region of the sporophyte the endodermis is well marked, and this is even 

 more the case in the root. In the mid region the xylem is separated from the endo- 

 dermis by a single layer of pericycle cells. 



About the time that the leaf emerges the first root of the bud begins to develop, 

 and, like the leaf, it seems to arise quite independently of the stem apex. The 

 tetrahedral apical cell is cut out from the cortical tissue of the root some distance 

 below the apex of the young bud, and as soon as the apical cell is established active 

 segmentation begins in the tissue below the bud and a strand of procambium is 

 developed, connecting the young root apex directly with the vascular bundle of the 

 primary root. Thus the vascular bundles of both the first leaf and the first root of 

 the young bud are directly connected with the primary root of the young sporo- 

 phyte and have nothing to do with the tissues in the apex of the stem of the bud, 

 which is still very small. 



