180 



the case figured, the vascular cylinder (plerome) becomes 

 widened abruptly a short distance below the apex, probably 

 primarily due to the rapid widening of the young lamina of 

 the leaf in which the reticulately arranged vascular l)iindles 

 are soon clearly differentiated. 



The fully developed cotyledon in what may be considered the 

 typical form of 0. moluccanum (Fig. 133) is more or less lanceolate 

 in outline. There is a central vein from which veins branch 

 on either side, connecting with the central vein by anastomosing 

 branches so as to enclose elongated meshes. In the form with 

 broader leaves, (Fig. 32) probably another species, the mid-vein 

 is more obscure and the areoles are broader and more numerous. 



As already indicated, the vascular strand of the young 

 sporophyte is continuous, and sections at different points show 

 essentially the same structure. The petiole of the cotyledon 

 (Fig. 142) which is traversed by two large lacunae shows the 

 axial bundle to be markedly collateral in structure. The xylem 

 consists of a group of about half a dozen tracheids at the inner 

 limit of the bundle whose endodermis is not clearly visible. 

 As the section of the bundle is made in the mid-region of the 

 sporophyte (Fig. 141) the only difference noted is a slightly 

 greater development of the tracheary tissue. The section of the 

 root presents almost exactly the same appearance as that of 

 the leaf. Whether we should call the root-bundle monarch or 

 collateral is merely a question of terms. In the mid-region 

 the eudodermis can be clearly made out, and it is seen that 

 the xylem is separated from it by a single layer of pericam- 

 bium cells. 



If the gametophyte of Ophioglossum is compared with 

 that of the other genera of the family it is found to be 

 most like that of Helminthostachys, with which it agrees 

 in its radial structure, while the gametophyte of Botrychium 

 is dorsi-ventral. The marked radial character of the pro- 

 thallium of all the species of Ophioglossum is noteworthy, 

 and it is probably to be attributed to the absence of light, 

 although this does not seem to apply to Botrychium, which 



