14 Harper and Dodge . — The Formation of the 
tests cannot be regarded as very convincing. The stages of formation of 
the cell-walls in the spores, and much more the membrane of the capillitial 
thread, are not easy to study as compared with the walls of pollen grains, 
bast fibres, &c. There are, however, at least the three clearly established 
facts just discussed, which bear on the chemistry of the processes involved 
in the formation of the capillitial thread. 
1. The process is initiated by the liberation of water and the formation 
of vacuoles. 
2. The vacuolar sap at first contains materials in solution, which are 
apparently precipitated in fixation, and which later disappear and probably 
furnish material for the capillitial wall and spirals. 
3. The spirals are laid down as organized material, in a definite form on 
the outside of the thread next to the vacuolar membrane, although function- 
ally, as we know from the elaters of the Liverworts, the position of the spiral 
on the inside of the thread would be also hygroscopically effective. 
The possibility that the chemical changes which lie back of these 
processes may produce volume changes and radial tensions such as Butschli 
assumes is certainly to be considered. The question as to whether the polar 
aster and the whole karyokinetic spindle figure may be regarded as due to 
streaming, and the further question whether the streams are directed towards 
or away from the centrosome, were considered by the earliest students of 
nuclear division (35), and the evidence on both sides has been many times 
discussed. The most recent papers on nuclear and cell-division throw 
little further light on the matter. Lundergardh (32-4) regards with 
scepticism all fibrillar structures, in the prophases and polar caps especially, 
as possible artifacts due to poor fixation, since they are not recognizable at 
once in the living cells. He finds that poor fixation gives more fibres than 
good fixation, but his elaborately worked out and vague conception of the 
directing and correlating influence of metabolic changes on the structures 
and movements involved in nuclear and cell-division is, as he freely confesses, 
as yet by no means illuminating. 
Lawson’s (29) conception that the spindle fibres are due to tensions set 
up in the cytoplasm as a result of the shrinkage of the nuclear membrane 
and that the fibres have nothing to do with the movements of the chromo- 
somes has been adequately criticized by Farmer (9) and Lundegardh (34). 
In the essential point of his conception of the origin of radial systems as 
a result of tensions developed about a region of shrinkage, Lawson (29), 
though not referring to him, follows the lines laid down by Butschli. While 
the possibility that such an explanation may apply in the case of the aster 
about the forming capillitial thread must be carefully considered, it alone is 
plainly inadequate to account for the development of the bipolar spindle, 
and the author does not attempt to apply it to the movement of the 
chromosomes. 
