1 84 
Beer . — On the Development of the Spores of 
which limit neighbouring vacuoles in consequence approach one another 
more and more closely. In sporangia, shortly before their dehiscence, 
the vacuolar cytoplasm has almost completely disappeared, but the plas- 
matic membranes are still present between the spores (Fig. 20). These 
can then, in nearly all cases, be seen to be double in structure owing to 
the complete approximation of the plasmatic membrane of adjoining 
vacuoles \ Starch grains can not infrequently be seen flattened out 
between the two adpressed membranes and, at the angles formed by the 
meeting of several vacuoles, nuclei occur. 
The nuclei show, at all stages, considerable variation in size, in form, 
and in character. In Botrychium Cardiff found that the nuclei underwent 
a very considerable increase in size during development ; thus in young 
sporangia he gives their size as 8 /x, whilst at a later stage he found them to 
measure 15-20 jix. In Helmmthostachys the general average of size of the 
tapetal nuclei appears to remain about the same at different periods of 
development. 
(a) Tapetal cells still intact .... 
(b) Young spores with thin , smooth exo spore 
(e) Spores with immature sculpturing on exospore 
(d) Spores just before dehiscence of sporangium 
13x11 j* 
1 3*4 x 10 /it 
12-6 x 9-6 fx 
13X11/X. 
The above figures are the averages calculated from a large number 
of countings and they show practically no alteration in the size of the 
tapetal nuclei. 
The form of the nuclei is very various. In the tapetal cells before 
disorganization and in the tapetal plasmodium before this flows between 
the sporogenous cells the nuclei are more or less oval in shape. The 
peculiar alteration in form which they often undergo as they pass within 
the sporangial cavity has already been described. In the later periods of 
development these nuclei are sometimes oval or spherical in outline ; often 
they are irregular in shape and occasionally their form is angular (Fig. 12). 
They possess, in most cases, a distinct nuclear membrane and are usually 
rich in chromatin ; several nucleoli can generally be seen in each nucleus. 
The chromatic granules are often closely packed (and the nucleus in con- 
sequence deep-staining) in the smaller nuclei, whilst in the larger nuclei 
the chromatin-grains are frequently separated more widely from one 
another and the nucleus contains more non-staining material. 
In Botrychium Cardiff found that ‘as the spores commence to separate 
in the tetrad, the tapetal cytoplasm has entirely filled the sporangium and 
many of the nuclei have begun to disorganize, though they seem unusually 
persistent and many are found after the tetrad is fully formed. Later, 
1 In consequence of the entire disappearance of the vacuolar cytoplasm which separated them 
from one another at an earlier stage. 
