242 Mr Gregory, Note on the Histology of the Giant, etc. 



I give in the table (p. 243) some measurements taken from 

 edge to edge of the group of chi'omosomes in the equatorial plane 

 of the heterotype division, but any difference in size thus indi- 

 cated is perhaps not very trustworthy, since it is slight and its 

 measurement depends entirely on reading by the eye to fractions 

 of the micrometer scale. 



But in the nuclei of the pollen mother cells and in the resting 

 nuclei of the various epithelial layers the differences indicated by 

 a comparison of the camera drawings are clearly borne out by a 

 comparison of the measurements (see table), all of which show the 

 same result, namely, that the nuclei of the Giant plant are, on the 

 average, larger than those of ordinary form, in the proportion of 

 from 4 to 10°/^ of each diameter. In the case of the developing 

 pollen mother cells great care was taken in choosing exactly com- 

 parable stages, though, as a matter of fact, there appears to be 

 only slight change in size when the cells have reached the stages 

 under consideration. Figs. 3 and 4 represent the stage whose 

 measures are recorded under the head " Prophase, with looped 

 thread"; figs. 5 and 6 represent those recorded under the head 

 " Prophase, diakinesis." The nuclei selected for measurement were 

 chosen at random, with the provision that any nuclei that showed 

 any signs of shrinkage or distortion during fixation, or were cut 

 by the knife, were excluded. In making the measurements the 

 divisions of the micrometer scale were read to fifths by the eye ; 

 to this extent therefore the measurements are only approximate, 

 but the preponderance of the measurements obtained for the 

 Giant over those obtained for the ordinary form, in the average 

 of a number of measurements, although not great, is, I think, too 

 consistent and regular to be accounted for by experimental error. 



Perhaps the clearest evidence is to be obtained from an 

 examination of the columnar cells of the ovule, to which reference 

 has already been made. Both in the measurements and in the 

 drawings these show a very consistent difference in size. Fig. 7 

 represents nuclei from this layer, the upper row being those of the 

 Giant, the lower row those of the ordinary form. It will be 

 noticed that the third and fifth are the largest nuclei in the 

 lower row; they are almost exactly equal in size to the first and 

 fourth of the upper row, which are, to say the least, distinctly not 

 the largest of that row. In the ordinary form some care was 

 exercised in the selection of the nuclei to be drawn, lest any 

 difference might be unintentionally exaggerated. The nuclei 

 shown in the figure were afterwards measured ; the average of 

 the measures of the six nuclei of the ordinary form was found to be 

 3*7 X 3*4 scale divisions, while the average in the case of the six 

 nuclei of the Giant was 3"9 x 3*7. If these figures are compared 

 with those given in the table, it will be seen that the difference is, 

 if anything, diminished rather than exaggerated in the figure. 



