258 Mr. W. H. Lang. Preliminary Statement on the 



other without the intervention of the vegetative organs. At first 

 sight such appears to be the case in the prothalli of the two species 

 described ; sporangia were present in close proximity to the sexual 

 organs, the vegetative organs of the sporophyte being, at most, repre- 

 sented by a mass of cells underlying the group of sporangia, and 

 even this distinction may not be recognisable beneath the single 

 sporangia on the edge of the prothallus. 



Several reasons may be adduced, however, against regarding these 

 phenomena as evidence that the alternation of generations found in 

 the ferns is not antithetic. In the first place, it is to be noted that the 

 two forms in which sporangia have been observed upon the gameto- 

 phyte are highly variable species, and that the varieties studied were 

 well-marked crested forms. Further, the conditions under which the 

 prothalli existed were in several respects unnatural. Among them 

 the fact that fertilisation was prevented by not watering the cultures 

 from above, and that a prolonged growth of the unfertilised prothalli 

 was thereby induced, is of special interest, for it appears that apogamy 

 is liable to occur under such conditions in ferns which, as a rule, 

 reproduce sexually. While these considerations do not of themselves 

 preclude deductions being made from these peculiar forms of repro- 

 duction, they necessitate especial caution in their use in the discusoion 

 of broad morphological questions. 



Further, a number of reasons exist for considering the production 

 of sporangia on the prothallus as a special case of apogamy. 

 In Scolopendrium vulgare a sporophyte may develope from the tip of 

 the cylindrical process. This may happen after a group of sporangia 

 has been developed. In one case two ramenta were present, one on 

 .each side of a group of sporangia; they were in every respect similar 

 to the ramenta which develope on the tip of the process when it is 

 being transfprmed into the apex of a bud. Whenever a group of 

 very young sporangia was seen it was situated upon the apex of the 

 lobe, and the sporangia were in a more advanced stage of develop- 

 ment the farther the group to which they belonged was removed 

 from the apex. This has been most clearly seen in the case of 

 Lastrcea dilatata in which no buds with vegetative organs have as 

 yet been seen, although in one case ramenta were associated with the 

 sporangia, but it also holds for Scolopendrium. The explanation of 

 these facts, which appears most probable, is that each group of 

 sporangia had occupied the apex of the process when very young, 

 and had become farther removed from this position as the process 

 continued to increase in length. It is uncertain whether this growth 

 is by direct continuation of the original growing point of the process, 

 or whether the development of a group of sporangia at the apex 

 necessitates the formation of a new growing point ; possibly both 

 forms occur. If the latter be the case a process on which several 



