1 76 Farmer and Digby .—Studies in Apospory and 
some of the criticisms which, on somewhat a priori grounds, have been 
urged against them. 
The prothallia on which our work has been almost exclusively based 
were given us by Dr. Lang, and they proved to be well-preserved for 
cytological investigation. We have not been successful in our efforts to 
raise material for ourselves, for spores sown in 1905 and 1906 for some 
reason failed to germinate 1 . 
As is well known, the prothallia of this variety of the Male Fern 
do not bear antheridia very freely, and the archegonia are wholly absent. 
In this respect it stands in sharp contrast with the variety polydactyla of 
Dadds, in which the sexual organs are produced abundantly, although 
no embryos are formed from the oospheres. 
We believe that the fusion of the nuclei of adjacent vegetative cells 
replaces, in each of these two Ferns, the normal sexual act, and we will 
now give in some detail an account of the process as it occurs in Lastrea 
pseudo-mas var. polydactyla , Wills, the original plant of which was found 
many years ago growing wild in Devonshire. 
The prothallia we used for this investigation were always mounted 
whole after staining, as with sections there is always a risk of misinterpreting 
the limits of particular cells, as well as the danger that the knife might have 
dislocated the nuclei from their original positions. The prothallia were 
stained in various ways, and on the whole we obtained the best results with 
Heidenhain’s Iron-Haematoxylin. 
The cells which are concerned in the migration are not limited to the 
thicker part of the prothallium. Those in the wings frequently afforded 
examples of the nuclear passage. It is, however, always in the younger 
regions of the plant that they occur, and it is useless to seek for them 
in the large full-grown cells at a distance behind the advancing margin. 
The first sign of migration on the part of a nucleus is seen in a change 
of form (Figs. 45-47). It commonly assumes an elongated shape with the 
pointed end directed to the wall that it is about to pierce. The nucleus 
in what we may term the receptive cell is usually round in form, and 
appears to be quiescent. When the end of the invading nucleus comes 
in contact with the partition wall, it obviously produces some change, 
probably by means of a fermentative activity, and the apical part of the 
nucleus slips through the narrow orifice thus made. The anterior end 
of the nucleus contains a darkly staining substance, and it gradually 
squeezes itself through the aperture. The whole process is a very clear 
case of chemiotaxis, as is evidenced by the very definite way in which the 
penetrating nucleus makes its way towards the nucleus of the receptive 
cell, and it is perhaps also further indicated by the accumulation of stainable 
1 Since this was written we have succeeded in raising a number of prothallia showing the 
apogamous peg. 
