iQiq] STEIL—PTERIS 47g 



It seems not improbable that the game tophy tic cells were 

 present at the earliest stages in the development of the embryo. 

 Since the sporophyte of Pteris sulcata is of apogamous origin, there 

 is an intimate connection between the cells of the gametophyte and 

 the sporophyte. These cells may be carried upward by the sporo- 

 phyte, and, retaining their power to divide, they may give rise to the 

 gametophytic portions which have been described. 



It has not so far been possible to state the conditions under 

 which apospory occurred in the culture of the prothalHa of Pteris 

 sulcata. All attempts to induce the phenomenon have failed. 

 Young sporophytes grown in subdued light produced no game- 

 tophytes aposporously. Portions of the leaves of young and old 

 sporophytes when placed on moistened sphagnum also failed to 

 develop prothalHa. 



The nuclear history of Pteris sulcata was not followed. It is 

 very probable, from studies so far made, that there is no change in 

 the chromosome number when the apogamous embryo originates. 

 It is also likely that when the gametophyte is formed in connection 

 with the embryo sporophyte there is no change in the chromosome 

 number. On account of the limited number of aposporous develop- 

 ments in the culture no favorable opportunity was presented to 

 count the chromosomes at a point in the hfe history when the 

 gametophyte originates. It is believed, however, that the game- 

 tophyte thus produced and one formed by the germination of the 

 spore have the same number of chromosomes. 



The changes which are involved in the formation of an embryo 

 of apogamous origin, except in the two Lastrea pseudo-mas varieties 

 described by Farmer and Digby, are unknown. In these ferns, 

 according to their description, fusion of adjacent prothallial cells 

 and their nuclei initiate the formation of the embryo with the 

 diploid number of chromosomes. It is certain from studies already 

 made that such changes are not involved in any of the apogamous 

 species which I have had an opportunity so far to investigate. 

 Until the exact nature of the changes which are involved when the 

 apogamous embryo originates are known, however, the origin of 

 the aposporous developments in Pteris sulcata cannot be explained 

 in a satisfactory manner. 



