THE GAMETOPHYTE 



15 



position in the humus about the plant, where they are found in the older parts 

 between leaves which must have been dead for many years, indicate that they are 

 very long-lived and, as we have seen, by the ready separation of the branches they 

 are easily propagated. 



THE HISTOLOGY OF THE GAMETOPHYTE. 



The younger portions of the growing branches are composed of thin-walled, 

 colorless parenchyma, whose cells have a conspicuous nucleus, and usually numerous 

 small starch granules. In the older portions of the gametophyte the tissue becomes 

 infected with the often-described endophytic fungus. Practically all of the cells of 

 the basal tuber are thus infested, but in the fertile branches the central tissue is 

 usually free from the fungus, and this medulla-like central tissue is surrounded by a 

 more or less definite mantle of cells, in which the endophyte is especially luxuri- 

 ant. The outermost cells are practically free from fungus, although new infections 

 probably may take place there through these outer cells. In 0. moluccanum the 

 endophyte is much less developed than in O. pendulum, this no doubt being corre- 

 lated with the much briefer duration of the gametophyte in the former species. 

 According to Bruchmann, the endophyte is strongly developed also in 0. vulgatum. 

 The endophyte, as in the other forms that have been studied, is quite absent from the 

 apical region of the branches. The limits of the infested zone are not very clearly 

 marked and any cell of the older tissue of the gametophyte may harbor the fungus. 



Fig. 5. 



A. Longitudinal section of gametophyte apex of Ophioglossum vulgatum. X150. 



B. Transverse section of gametophyte apex, u, the apical cell. 



C. Archegonium. X225. 



D. Two free spermatoioids. X550. (All figures after Bruchmann.) 



The apical cell in 0. pendulum is usually a four-sided pyramid, and not tetra- 

 hedral, as it is in 0. vulgatum. In longitudinal section (fig. 4, D), the apical cell 

 appears triangular with a fairly regular segmentation, but there is also active division 

 in the adjacent tissue and apparently the segmentation of the apical cell is not very 

 rapid. Cross-sections show the apical cell to be approximately four-sided (fig. 16, A), 

 but the sides are not always of equal length and sometimes it is almost triangular in 

 outline; possibly it may be that in some cases, as in 0. vulgatum, it is tetrahedral. 

 There seems to be no absolute rule, however, as to the succession of divisions in the 

 young segments. A more or less definite superficial layer arises from the first 

 periclinal divisions, but anticlinals follow rapidly. 



