ASEXUAL GROWTH FROM PROTHALLUS OF PTERIS CRETICA. 267 



cretica and Aspidium molle had been sown. At the begm- 

 ning of the investigation there were a number of seedlings 

 of both the above-named species which were considerably- 

 advanced in growth ; and in addition there were numerous 

 prothalli, from some of which young plants had begun to 

 grow, and others still younger on which no incipient plant- 

 lets could be discovered with the naked eye. A search was 

 made among the latter for prothalli in a condition suitable 

 to demonstrate the earliest stages of growth after the fertilisa- 

 tion of the archegonium. Some of these prothalli were 

 normally developed, having both antheridia and archegonia, 

 from which occasionally an embryonal growth was seen. 

 During the search, however, numerous specimens were found 

 presenting the anomaly of scalariform ducts in the substance 

 of the prothallus ; and such prothalli, when still further de- 

 veloped, showed that the young fern-plantlets produced by 

 them were the result of a direct budding of the cells, and 

 not of the changes caused by the act of fertilisation in a single 

 embryonal cell. The number of cases in which the above- 

 mentioned peculiarity was manifested was about fifty ; but, 

 undoubtedly, the actual number was greater, inasmuch as 

 some of the young fern-plantlets in the pot, which were too 

 old to allow one to say whether they had been regularly 

 developed (that is, by growth from an embryo) or not, probably 

 belonged to the number of those developed by direct bud- 

 ding. The shape of the prothalli was, as usual, more or 

 less obcordate ; and those in which the anomaly presented 

 itself, although variable in outline, were narrower than the 

 others. This narrowness may have been only accidental and 

 the result of crowding in the pot, as very often happens in 

 the cultivation of ferns. In a single case one side was 

 developed into a sort of secondary prothallus. The cells 

 of the prothalli were perhaps somewhat paler than usual; 

 and those which, near the concavity of the heart, are gene- 

 rally more numerous than in other portions and isodiametrical, 

 were here much longer than broad, — that is, longer in the 

 direction from the centre of the prothallus towards the concavity. 

 As is well known, fern prothalli are generally heart or kidney- 

 shaped, and the two sides composed of a single layer of 

 polygonal cells, the centre of a portion decidedly thicker and 

 consisting of several layers, which we may call the cushion ; 

 and in this last-named portion are situated the archegonia, 

 while the antheridia, are much more widely dispersed, being 

 found also in the lateral lobes. As before said, the most 

 striking feature of the abnormal prothalli was the presence 

 of a scalariform duct in the cushion a short distance back of the 



VOL. XIV. NEW SER. S 



