302 Marquette, Manifestation of polarity in plant cells which usw. 



there is no doubt that they are differentiated structures of the cell 

 which multiply by successive bipartitions. Furthermore the relations 



of these bodies and their motions to the formation and orientation 

 of the spindle fibers indicate that they are most intimately connected 

 with spindle formation. 



Isoetes is somewhere on the border line between pteridophytes 

 and phanerogams and it niight possibly be assnmed that in Isoetes 

 we have a transition from a cell stmctnre 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 head of a more or less independent develop- 

 niental series, so that the conditions found in its cells may quite 

 possibly be 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 spermatozoicls, similar requirements and environ- 

 mental conditions calling forth similar structures. 



In 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 lucida. 



Figs. 1—7 are taken from cells of young leaves of Isoetes lacustris and are 

 magnified 1250 diameters. Fig. 8 is from a spore-mother-cell of Equi- 

 setum hyemale, magnified 700 diameters. Fig. 9 from a spore-mother- 

 cell of Marsüia quadrifolia. mag. 700 diameters. 



Fig. 1. „Resting'- cell, the nucleus lies close to the last formed cell wall. 

 The stareh 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 persistiug furrow formed in the 

 nucleus by the separating polar structures. 



Fig. 4. Polar structures withdrawn from the nucleus, spindle fibers appearing, 

 extending between the polar structures and the nucleus. The nuclear 

 membrane disappearing. 



Fig. 5. Completed spindle. equatorial plate stage. 



Fig. 6. Late diaster showing well developed connecting fibers; the poles of 

 the spindle still persisting. 



