466 Stevens. — Spore Formation in Botrychium virginianum . 
and results in a common tapetal plasmodium by the close of the first 
prophase. The cells of the tapetum are easily distinguished from the 
spore-mother-cells by their coarser-grained cytoplasm, their irregular size 
and form, and their smaller nuclei with close-meshed reticulum and numerous 
nucleoli. 
Following now the behaviour of the spore-mother-cells : as the pro- 
phase advances the nuclear thread becomes thicker, evidently by shortening 
through longitudinal contraction, and clearly not by the approximation and 
apparent fusion of parallel parts of the thread as described by Berghs (’ 04 ) 
for the microspore-formation of Allium fistulosum. I have examined my 
preparations carefully to see if this fusion occurs, and while I can find 
numerous instances of the close approximation of the parts of the nuclear 
thread, I do not find these parts fusing, but do find them thickening without 
fusion until the stage represented in Fig. 3 appears. While the nuclear 
thread is thickening it is becoming more and more erythrophil, and retains 
the safranin in preference to the gentian-violet (when the triple stain 
safranin-gentian violet-orange is used) some time before its separation into 
chromosomes. Although my preparations show a close succession of stages 
in the prophase I have not been able to find the gamosomes recently 
described by Strasburger (’ 04 ) for Thalictrum purpurascens. It may be 
that in Botrychium their isolation from the linin framework takes place 
earlier during the long winter rest of the spore-mother-cells. 
When the nuclear thread first segments into chromosomes the latter 
appear from various points of view, as seen in Fig. 4, where a , b , c, and d 
show clefts that have evidently arisen from longitudinal fission; e>f,g y h, 
and i show chromosomes bent or doubled in various degrees ; and j shows 
an end view of such a figure as d or h y one arm being longitudinally split 
and the other not. On comparison with the work of Farmer and Moore (’ 03 ), 
Strasburger (’ 04 ), Gregory (’ 04 ), and preparations illustrating spermato- 
genesis in the Acrididae which Dr. McClung has kindly shown me, where 
the different prophase stages can be seen with remarkable clearness, I am 
led to the conclusion that these bent chromosomes are or become divided 
by transverse fission at the apex of the bend. The chromosomes of Fig. 31, 
culled from stages represented by Figs. 16 and 17, indicate that this fission 
has taken place, and they are very similar to Strasburger’s Fig. 5, where 
with a better subject he is confident of a transverse fission. My Fig. 18 
indicates that in the anaphase the separation of the chromosomes is to take 
place in the plane of transverse fission. The longitudinal division begun in 
the early prophase, and clearly seen in Fig. 4, is lost sight of and only slightly 
indicated in the cross-shaped chromosomes of Fig. 18. In the anaphase 
(Figs. 33 and 34) all trace of the longitudinal division is lost. It will 
be seen that Botrychium is not a good subject to bring in evidence regard- 
ing the vexed question of the manner of chromosome-division. So far 
