Beer, — Studies in Spore Development . II. 713 
pointed out before, it is not unlikely that some confusion may have arisen 
in the past through this behaviour of the loops and their resemblance to 
a double spireme. 
In Fig. 15 I have drawn a long loop of Crepis taraxacifolia in which 
the sides have come closely together. In Fig. 14 is shown a nucleus 
in which several such loops and their simulation of a double spireme 
will be evident at once. It was quite easy, nevertheless, to entirely satisfy 
oneself that the structures in this nucleus were actually closed loops. 
In some sections one can without difficulty observe the separation 
of the loops from their meeting point at the common centre (Fig. 19). At 
first they remain grouped together with their proximal ends free from one 
another but still directed towards a common centre. The distal ends of the 
loops at this time usually have their limbs still united. As the loops become 
separated from the common centre from which they all radiated just before, 
the two limbs tend more frequently to become twisted about one another 
than was the case at an earlier stage. 
The isolated loops continue to separate from one another and to travel 
towards the periphery of the nucleus. Many remain as loops closed at one 
end, others break across the loop and the two limbs are then independent 
of one another, although they remain more or less closely associated 
together (Fig. 20). 
Diakinesis. 
The two limbs of the loops are for a time long and comparatively 
slender, but as they reach the nuclear membrane, and there take up the 
position characteristic of the nucleus during diakinesis, they shorten and 
become very much thicker. The two arms of the loops are variously 
arranged with regard to one another. They sometimes appear as crosses, or 
as rings, or loops still unbroken at one end, or as two rods which lie side by 
side or which have become closely twisted together. In fact, all the different 
forms which have been described by cytologists in dealing with the bi- 
valent chromosomes during the diakinesis of various plants, can be found 
in the appearances presented by the two arms of the loops of the Com- 
positae. It appears to me impossible to doubt that the arms of the 
loops of these plants correspond to single chromosomes, and that each 
association of the two limbs of a loop forms a bivalent chromosome 
(Figs. 20-3). 
In Matricaria (Fig. 23) by far the most usual form assumed by the 
chromosomes during diakinesis is that of closed rings. In Tragopogon 
and in the two species of Crepis , however, the paired chromosomes occur 
as often in the shape of a cross, or a loop open at one end, or twisted 
rods free at both ends, as in that of the closed ring. 
