ORIGIN AND RELATIONSHIPS OF THE EUSPORANGIATAE 



211 



phyte, and in Ophtoglossum much the same thing occurs in the cotyledon, although 

 at first this grows from a single apical cell. It is probable that in the ancestors of the 

 Ophioglossaceae this upper conical portion of the embryo was developed directly 

 into a spore-bearing organ. There is, however, a marked difference which soon 

 appears, viz, the development of a true root in Ophioglossum. This root, pushing 

 down through the foot, penetrates the lower side of the gametophyte and places the 

 young sporophyte directly into communication with the water supply from the earth, 

 and thus the latter becomes entirely independent. Were the large sporophyte of 

 Anthoceros to develop a similar root from the basal meristem, it also would become 

 entirely self-supporting. Indeed, so marked are the resemblances in the early stage of 

 development that they make the inference almost irresistible that the Ophioglossaceae 

 must have descended from some simpler forms whose sporophyte bore a strong 

 resemblance to Anthoceros. This " pro-Ophioglossum," if we may call it so, pre- 

 sumably produced spores upon the first leaf, instead of its being a sterile cotyle- 

 don as in the existing forms. From a study of the development of the sporophyte 



Fig. 192.— Comparison of sexual organs in Anthocerotaces and Marattia. 



A. Longitudinal section of the thallus of Anthoceros pearsoni Howe, showing an antheridium mother cell, 

 with the superimposed cover cell (d). 



B. An older antheridium within a cavity covered by a double layer of cover cells. 



C. Young archegonium of Megaceros tjihodensis Campbell, a form closely related to Anthoceros. 



D. Sections of young antheridia of Marattia douglasii Baker. The inner ceU divides at once into the sperm 

 cells, and the cover remains single-layered, d, the cover. 



£. Young archegonia of Marattia douglasii. b, the basal cells of the archegonium; d, neck. 



O. moluccanum, it may be inferred that this ancestral form had no stem, but 

 consisted simply of this spore-bearing leaf and a root. The sporangia were presum- 

 ably simpler than in the existing forms of Ophioglossum, and perhaps intermediate 

 in character between such sporangia as those of the smaller species of Ophioglossum 

 and the imperfectly segregated spore groups which occur in the Anthocerotes. 



Not only does the sporophyte of Anthoceros show important resemblances to 

 that oWphioglossum, but the development of the sexual organs also shows striking 

 analogies. The archegonium, unlike that of other Bryophytes, is sunk below the 

 surface in much the same fashion as that of the eusporangiate ferns, and the short 

 neck of the archegonium in the latter is probably to be compared to the four terminal 

 neck cells which may occur in the Anthocerotes (fig. 192). The endogenous anther- 

 idia of the Anthocerotes also may perhaps be compared to the sunken antheridia of 

 the eusporangiate ferns, and in their early stages the resemblances are very close. 



in 



