710 Beer. — Studies in Spore Development . //. 
I have found it very difficult to determine whether this spireme forms 
a continuous thread or whether it is segmented into several parts. In the 
majority of cases I can find no evidence of the existence of free ends (except 
where these were obviously due to the microtome knife), and the spireme 
appears as one long, continuous, much-wound thread. A few nuclei were, 
however, met with in which the existence of a continuous unsegmented 
spireme appeared somewhat more doubtful (Fig. io). It is possible, how- 
ever, that another explanation may be found for these rather exceptional 
cases in which free ends of the threads were apparently present. In any 
case, the segmentation of the meiotic spireme of these plants, if it really 
occurs at this stage, is very difficult to see, and contrasts strikingly with the 
obviously segmented spireme of the somatic divisions of the same plants. 
In the lily, as well as in a large number of plants and animals, a longi- 
tudinal split has been described in the spireme. This longitudinal division 
of the spireme has received very contrary interpretations at the hands of 
various investigators. Some regard it as a precocious division of the spireme 
which only reaches its consummation during the homotype separation of 
the chromosomes. Other cytologists look upon the split in the spireme, 
not as a true division of that filament, but as the approximation and con- 
jugation of two separate and independent threads. In the case of the 
Compositae a longitudinal split of the spireme has been described, and 
very conspicuously figured by both Rosenberg (19, 20) and Lundegardh (15). 
These writers adopt the view that the division in the spireme is not a true 
division, but that it really represents the approximation of two independent 
spiremes. 
I have devoted much time and care to the study of this matter, but 
although many hundreds of sections of pollen mother-cells containing the 
hollow spireme, either completely developed or still unfolding from the 
synaptic knot, have been passed in review, I have not succeeded in finding 
a single unquestionable example of a split spireme ! The filament is com- 
paratively thin in these plants, and it is not easy to determine whether the 
row of chromomeres is single or double ; but, however this may be, I have 
never found an instance in which the spireme was divided into two halves 
which divaricated in the slightest degree from one another. Other plants 
belonging to quite different orders to the Compositae have been very 
thoroughly studied by other cytologists, and the same difficulty in demon- 
strating a longitudinal division of the spireme has been met with. In the 
species of Oenothera examined by Davis (3), that writer was unable to find 
a longitudinal split in the spireme. After pointing out that such a split 
may still quite possibly be found in the future, he adds, ‘ but, as previously 
noted, the writer has found no evidence that such a division takes place or 
that there is a fusion of parallel spiremes.’ 
It would seem then that there is a good deal of difference in the 
