On the Archesporial and Meiotic Mitoses of Osmunda. 
BY 
L. DIGBY. 
With Plates VIII-XII and one Figure in the Text. 
Introduction. 
/<0 
V 
^ s oman 
JUN 
! f, 'on a l 
T HE sporogenous tissue of Osmunda has been a favourite object for 
cytological study ; not only is it often used for class demonstra- 
tion, but many cytologists have chosen it for critical examination, and the 
resulting literature is conflicting in its conclusions. The large size of the 
nuclei and the remarkably clear and well-defined character of the division 
figures suggest, on a superficial survey, an easy solution to some of the 
more complex problems connected with karyokinesis, but, on closer inspec- 
tion, it will be found that, although the general landmarks of nuclear 
division are certainly strikingly portrayed, yet factors £xist which make 
the elucidation of the deeper controversial questions exceedingly difficult. 
In the first place, the arrangement of the sporangia affords no clue as 
to the stages of nuclear division in their contained archesporial or spore 
mother-cells, whereas in many tissues the position of the nuclei is a useful 
guide in identifying the sequence of the individual phases. For instance, 
longitudinal sections of anthers generally show the nuclei near the base to be 
slightly less advanced than those near the apex, and those more centrally 
placed to be in an intermediate stage ; whilst in transverse sections the two 
outer loculi may be seen to be in advance of the two inner ones, and of each 
respective pair one loculus may be slightly ahead of the other in the pro- 
gress of nuclear division. Osmunda , on the other hand, gives no such lead, 
for contiguous sporangia may present widely separated stages. Matters 
are further complicated owing to the exceeding rapidity with which some of 
the most critical stages are passed through. Probably others have had a 
similar experience to that of the writer, and have been baffled year after year 
in the attempt to elucidate the origin of the heterotype chromosomes owing 
to the elimination of certain particular phases in the available material which 
have ultimately proved to be the key to the problem. And lastly, Osmunda 
is difficult to fix satisfactorily. It is simple to achieve a somewhat flashy 
hard fixation which displays familiar stages well, but it is unsatisfactory for 
those of crucial importance such as post-synapsis and pre-second con- 
traction. 
[Annals of Botany, Vol. XXXIII. No. CXXX. April, 19x9.] 
