Marquette, Manifestations of polarity in plant eells which usw. 285 



held quite generally amongst botanists that in the vascular crypto<- 

 gams and in tlie Phanerogams the karyokinetic spindle develops 

 witliout the participation of a centrosome. 



It shoulcl be mentioned that (luignard, 1 ) who more than anyone 

 eise has bnsied himself with the question of the existence of centro- 

 somes in the higher plants, has songht to bring liis earlier Statements 

 into harmony with the discovery of the multipolar stage in spindle- 

 development by the assumption of multiple centeis. In so doing, 

 however, he dispensed with one of the most important character- 

 istics of the centrosomes as they are known in the animal cells: 

 that is, their constant bipartition and the immediate establishmenl 

 of a bipolarity of the cell as soon as the daughter centers separate. 



According to the present most fully developed conception 

 concerning the processes of division in the higher plants, that is. 

 according to the „kinoplasm" theory as advanced by Strasburger 

 and Ins pupils, we have in the cytoplasmic flbers or rays units 

 which in coordination with one another go through the various 

 movements and transpositions necessary to produce the bipolar 

 spindle. At no time during the whole process do structures appear 

 which could be compared with centrosomes. Not only is nothing 

 to be seen of a central body, but the assumption of its invisible 

 presence is entirely superfluous. The übers considered as co-ordi- 

 nated units give just as satisfactory an account of the processes 

 observed in spindle formation as can be given by assuming the 

 presence of a minute granule which in some mysterious manner 

 controls the activities of the flbers. 



The question still remains as to how on the kinoplasm hypo- 

 thesis the flbers so co Ordinate their activities as to constantly 

 produce a bipolar Organisation and consequent bipartition of the 

 mother cell, and further, as to how the process of division with 

 the presence of a central body, whatever its function, as found in 

 the algae and fungi has passed over into the type of division 

 witliout a central body as found in the higher plants. From this 

 standpoint I have undertaken the studies on nuclear and cell 

 division in Isoetes described below. 



Leare a wider space between these two paragraphs. The material 

 for this work was collected at Devils Lake, Wisconsin, where 

 Isoetes lacustris grows abundantly, putting forth new leaves from 

 the beginning of spring tili late in the fall. Of the various fixing 

 fluids in common use, Flemming's stronger chrom-osmiuni-acetic 

 mixture gave the best results. The material was imbedded and 

 sectioned in the usual way. The sections were stained for the 

 greater part either with Flemming's triple stain or with Heiden- 

 hain 's iron haematoxylin. 



Leaves which have reached a length of about 5 mm show a 

 large number of nuclear and cell divisions and even a hasty survey 



] ) Guiguard. L.: Les centrosomes chez les vegetanx. (Compt. Rend. 

 TCXXV. 1897. p. 1148.) Les centres cinetiques chez les vegetaux. (Ann. d. Sei 

 Nat. JBot. 8e Ser. TVI. 1897. p. 177.) 



