528 SIGNIFICANCE OF CAMBIUM 



initials is not associated with a tetraploid or polyploid condition. 

 Nor is it a concomitant of a marked increase in the size of the indi- 

 vidual chromosomes, for I have repeatedly found small ray initials 

 in which the chromosomes were fully as long and thick as those of 

 adjoining large, elongated initials. The staining reactions of the 

 various types of initials indicate that the chromatic material is more 

 concentrated in the smaller than in the larger nuclei except during 

 certain stages of karyokinesis; and that the increase in the size of the 

 nuclei is due primarily to an increase in the volume of achromatic 

 substances. Although there is no constant and striking difference in 

 the number and size of the chromosomes in the large and small ini- 

 tials, the volume of the nucleoli is conspicuously greater in the larger 

 cells (Figs. 3, 4, 5, and 6). This increase is associated with a corre- 

 sponding increase in kinoplasma during karyokinesis and cytokinesis. 

 My observations upon Pinus strobus, therefore, do not support 

 Strasburger's and Winkler's conclusions in regard to the constancy of 

 "specific" cell sizes and nuclear sizes in the meristems of plants and 

 are in opposition to Winkler's assumption that giant cells are hyper- 

 chromatic. In lateral meristems there are relatively great variations 

 in cell size without corresponding changes in the number of chro- 

 mosomes. In other words, in dealing with the nucleocytoplasmic- 

 relation it is essential to distinguish between (1) those cases in which 

 there is a correlation between cell size, nuclear size, and chromosomal 

 mass, and (2) those in which chromosomal number (chromosomal 

 mass) is constant and nuclear size and cellular size are variable. 



Karyokinesis and Cytokinesis. 



In the gymnosperms, as illustrated by Pinus strobus, the polar axis 

 of the division figure usually does not stand at right angles to the 

 long axis of the protoplast, but is placed diagonally across the cell 

 (Fig. 7). This position of the karyokinetic figure is not an artifact, 

 i.e. due to displacement of an ordinary spindle, since the whole 

 figure is asymmetrically developed in conformity with its diagonal 

 position. The formation of a cell plate, starting from one of these 

 obliquely placed spindles, is a truly remarkable cytological phenome- 

 non. The spindle becomes greatly extended laterally by the addition 

 of peripheral "fibers," and gradually assumes a more or less curved 



