3o8 BOTANICAL GAZETTE [may 



an instance in which the apogamous development of the sporophytc is 

 not preceded by apospory. The prothalha in these forms are pro- 

 duced after normal sporogcnesis and consequently they contain the 

 gametophytic number of chromosomes. The authors claim to have 

 found in certain vegetative cells the fusion of two nuclei, one of which 

 has entered the cell from an adjacent one, and that the sporophytc 

 develops from the region of the prothallium where this fusion occurs. 

 They regard this fusion of two vegetative nuclei as a substitute for 

 normal fertilization. A similar instance of the fusion of two vegetative 

 nuclei is given by Blackman (4) for Phragmidium, who regards (4, 

 S) the process as a reduced form of fertilization. The conjugated 

 nuclei divide simultaneously through a long series of nuclear divisions, 

 from the formation of aecidiospores to that of teleutospores, where 

 the last pairs unite to form the single fusion nuclei within the teleuto- 

 spores. There is much evidence that the period in the lifc-histor>' 

 characterized by the presence of the paired nuclei represents a sporo- 

 phytic phase. Thus the fusion of the two nuclei in vars. polydadyhi 

 and the pairing condition of the two nuclei in Phragmidium may 

 support as a working hypothesis the assumption that a nucleus \m ^ 

 the sporophytc number of chromosomes is necessary for starting e 

 sporophytc generation. 



The condition shown in the apogamous Nephrodium is entire > 

 different from anything yet recorded for plants. The prothalha are 

 developed after normal sporogcnesis and their nuclei retain t e 

 gametophytic number of chromosomes. The sporophytc then appears 

 as a vegetative outgrowth from the prothallium, without any visi^ c 

 change in the nuclei, so that there is estabHshed a sporophytc wit 

 the gametophytic number of chromosomes. Farmer and Digby (24 

 have suggested that the number of chromosomes, approximate} 

 60, which is found throughout the life-cycle in Lastrea pseudo-mas 

 var. cristata apospoya may be the gametophytic number in the t\pe 

 species, that is 72, and that this variety might have arisen from norma^ 

 prothalha of the type species through apogamy. Williams (74 

 gives an instance of true apogamous development of the egg 

 Dictyota, which is as yet the only type among algae where the nuc ear 

 conditions of apogamy are known. In Williams' cultures the ger- 

 mination of the unfertilized egg with 16 chromosomes, the gameto- 



