Beer . — Studies in Spore Development . III. 649 
spireme to be seen according as we examine a median or a peripheral 
section of the nucleus. 
In Fig. 18 I have represented a median section of a nucleus, where it 
will be seen that the filaments appear to be arranged without order. In 
Fig. 19 is shown a peripheral section through a neighbouring nucleus at 
precisely the same stage. Here it will be observed that there is a very 
definite order in which the threads are grouped, and that they exhibit 
a certain amount of parallelism with one another. 
Another feature of some importance is very evident in the spireme of 
this plant, and that is the discontinuity of the thread. It is only necessary 
to glance at any of the figures which I have given (Figs. 18, 19, 30, 27) to 
see at once that free ends of the filaments are of frequent occurrence, and 
that the spireme is segmented up into comparatively short lengths. Up to 
this time the cells of the sporogenous tissue have remained united as a single 
block of tissue surrounded by the tapetum. Each spore mother-cell is 
bounded by a thin wall, which gives the reactions characteristic of pectic 
bodies. 
During the stage of the spireme, however, the membranes separating 
the spore mother-cells become split and the cells begin to separate from 
one another. Each mother-cell is at this time still covered by a delicate 
film of membrane which is the remains of the septum which formerly 
separated one cell from another. 
Each spore mother-cell rounds itself off as it becomes isolated from its 
neighbours. In the meanwhile the tapetal cells have also lost the mem- 
branes which separated them from one another, and have flowed together 
to form a richly nucleated plasmodium. This tapetal plasmodium now 
begins to penetrate into the interior of the sporangium and to surround the 
sporogenous cells as these become isolated. As I pointed out in my 
previous note, and as Hannig ( 3 ) has confirmed, the tapetal cytoplasm first 
makes its way between the sporogenous cells, and the tapetal nuclei follow 
suit slightly later. 
In somewhat older spore mother-cells the nuclear spireme has increased 
a little in thickness and become more retentive of chromatic dyes. In such 
nuclei the longitudinal division of the spireme can usually be again seen 
(Fig. 20). This stage immediately precedes a period during which the 
nuclear contents lose their regularity of outline and become drawn together. 
During this phase, which may be called that of the 4 second contraction * 
(although there is not such a profound massing of the nuclear contents as is 
the case in some other plants ), 1 it often becomes very difficult to correctly 
interpret the changes which are taking place within the nucleus. It is only 
when the almost fully developed bivalent chromosomes emerge from the 
confusion that it again becomes easy to follow the course of events. 
1 Cf. Miss Digby’s figure of Primula verticillata , for example, ( 2 ) Plate XLII, Fig. 46. 
