302 Marquette, Manifestation of polarity in plant cells which usw. 
tliere is no doubt tliat tkey are differentiated structures of the cell 
which multiply by successive hipartitions. Furthermore the relations 
of these bodies and their motions to the formation and Orientation 
of the spindle fihers indicate that they are most intimately connected 
with spindle formation. 
Isoetes is somewhere on the border line between pteridophytes 
and pkanerogams and it might possibly he assmned that in Isoetes 
we haye a transition from a cell structure with well defined central 
bodies as found in some algae and fungi to a cell structure appar- 
ently without central bodies or anything corresponding to them 
as found in the spermatophytes. Still, the data we have seem to 
show that in the pteridophytes aside from the universal presence 
of blepharoplasts a cell Organization essentially similar to that of 
the spermatophytes prevales. It is to be noted of course that 
Isoetes is not among the direct ancestors of the spermatophytes but 
Stands rather at the liead of a more or less independent develop- 
mental series, so that the conditions found in its cells may quite 
possibly he the outcome of another line of development from the 
lower forms with central bodies than that followed in the deve¬ 
lopment of the spermatophytes. It is always to be further remem- 
bered that physiologically and anatomically equivalent structures, 
apparently may arise independently in widely separated organisms, 
note for example the similarity in structure and formation of some 
plant and animal spermatozoids, similar requirements and environ¬ 
mental conditions calling forth similar structures. 
ln conclusion I wish to heartily thank professor E. A. Harper 
for the encouragement and aid he has given me in the preparation 
of this paper. 
Explanation of Figures. 
The figures were drawn with the aid of the camera lueida. 
Figs. 1—7 are taken from cells of young leaves of Isoetes lacnstris and are 
magnified 1250 diameters. Fig. 8 is from a spore-mother-cell of Equl- 
setum hyemale, magnified 700 diameters. Fig. 9 from a spore-mother- 
cell of Marsilia quadrifolia. mag. 700 diameters. 
Fig. 1. „ßesting“ cell, the nucleus lies close to the last formed cell wall. 
The starch containing polar structure extends out from the polar de- 
pression in the nucleus. 
Fig. 2. Division of the polar structure, the separating halves drawing through 
a depression or furrow in the nucleus. 
Fig. 3. The daughter polar structures at opposite sides of the nucleus, closely 
pressed against it. a, section of the still persisting furrow formed in the 
nucleus by the separating polar structures. 
Fig. 4. Polar structures withdrawn from the nucleus, spindle fibers appearing. 
extendmg between the polar structures and the nucleus. The nuclear 
membrane disappearing. 
Fig. 5. Oompleted spindle, equatorial plate stage. 
Fig. 6. Late diaster showing well developed connecting fibers; the poles of 
the spindle still persisting. 
