THE DEVELOPMENT OF THE KARYOKINETIC 



SPINDLE IN THE POLLEN-MOTHER-CELLS 



OF LAVATERA.i 



BY EDITH SUMNER BYXBEE. 



Plates X-XIII. 



The way in which the spindle is formed varies widely in 

 the different families of plants that have been studied. In 

 the generative cells of higher plants, the spindle seems to 

 be always multipolar at first, but the formation of the poles 

 may proceed in several different ways. With a view to 

 shedding further light on this question, the pollen-mother- 

 cells of a species of JLavatera were selected for study. ^ 



This plant blooms throughout the year, so that the mate- 

 rial is plentiful at all times, while the arrangement of the 

 flowers in dense racemes and the number of anthers in a 

 flower make it easy to obtain cells in all stages of division. 

 The pollen-mother-cells are large. They may be examined 

 before preserving, so that much time is saved. The flowers 

 were usually gathered in the morning, as it was found that 

 then the cells were dividing more rapidly. The anthers 

 were examined by crushing them, either with or without the 

 addition of one per cent, glacial acetic acid. All heads in 

 a favorable condition were then immediately dropped into 

 the fixing fluid. It may be mentioned here that all the more 

 striking appearances observed in preserved material were 

 also seen in the fresh. The granular zone, especially, stands 

 out with great distinctness by reason of the strong refrac- 

 tive properties of its granules. 



• Contributions from the Botanical T^aboratories of the University of California, No. 

 13. Presented for the degree of Master of Science, Prepared under the direction of Dr. 

 W. J. V. Osterhout. 



- Owing to the destruction of the plants, it has been impossible to determine the spe- 

 cies with exactness. It is probably either Lavatera ungukulata Desf. or L. micans L. 



[63] October 29, 1900. 



