250 BOTANICAL GAZETTE [ APRIL 
diversity may be found within a single sporangium. igs. 53 a, 
6, c, and 54 a, 6, c, were all taken from the same section of the 
same sporangium. Probably the variation in this respect is not 
of great importance except as indicating that the divisions of 
Isoetes have not acquired so. definite and settled a character as 
those of most other plants. 
Although the nuclei of the young spores may arrange them- 
selves in typical tetrahedral fashion, there is an important differ- 
ence between their relation here and in the tetrahedral divisions 
of dicotyledons, Lycopodium, etc. In these it is well known that 
all four nuclei (of such a stage as fig. 5¢) become connected by 
spindle fibers, and that the walls separating the spores are 
formed in connection with the thickening of the cell plates of 
the six spindles. In spite of careful search I have been unable 
to find in Isoetes any such sextuple spindles. The daughter 
nuclei are connected only in pairs, as in fig. 53 or 54. In what 
way the spore walls originate in such cases I cannot conjecture. 
It seems certain they are not formed in connection with the 
achromatic figures, unless it is possible that the cell plate, which 
is always present in the first division, may make its influence felt 
later on, and ultimately serve as the basis of the wall. 
The young tetrads soon fall apart, and the individual spores 
lose their angularity and round up, still retaining traces, how- 
ever, of the bilateral shape impressed upon them by their 
manner of origin. When once the permanent form is assumed 
there is little further increase of size. The mature spores of 
fig. 56 are little larger, it will be seen, than the newly formed 
spores of fig. 57. 
An interesting phenomenon in connection with the micro- 
spores is the extreme smallness of their nuclei in comparison 
with those of the mother cells. One would naturally expect the 
relative volumes to be about 1:4, or the relative diameters to be 
about 3:5 (since f= nearly). But the volume of the micro- 
spore nucleus is really no more than one twelfth of this est 
mate; or to express the comparison in another way, it would 
need the nuclei of fifty microspores combined to equal the 
