240 Mr Gregory, Note on the Histology of the Oiant 



to Mr Leonard Sutton for further information on this point ; he 

 writes: "With regard to the size of the seeds, we do not find 

 much difference in the Stellata forms, but in the Florist's type, 

 seed of the Giant varieties, though variable from year to year, is 

 always larger and flatter than that of the smaller flowered sorts." 



At Professor Bateson's suggestion I have made observations 

 with a view to comparing the nuclei of the two forms. The 

 plants chosen for the purpose were (1) a Giant White Star with 

 dark red stems, and (2) a White Star of the ordinary habit, but 

 closely resembling the Giant in all other characters. For both of 

 these plants I am indebted to Messrs Sutton of Reading. 



The primary object of the investigation was to discover whether 

 there might be a difference in the number of the chromosomes in 

 the two forms, an idea suggested by the results of Miss Lutz* and 

 Gatesf in Oenothera gigas. Upon this point the answer is definitely 

 in the negative; the number of the chromosomes is the same in 

 both forms oi Primula sinensis, viz. 12 (reduced) and 24 (somatic). 

 The reduced number of chromosomes is shown with quite diagram- 

 matic clearness in sections transverse to the spindle at metaphase 

 or anaphase of either of the two meiotic divisions (figs. 1 and 2). 

 In the somatic divisions the chromosomes are more closely crowded 

 and their precise number is less easy of determination; but several 

 counts have given numbers ranging from 22 to 24, and there can 

 be no doubt, I think, that the number may be correctly stated at 

 24. I have no evidence which suggests that there is any tendency 

 to variation in the number of chromosomes which occur in the 

 somatic mitoses found in various regions of the floral organs. 



But although the two forms are alike in the number and form 

 of the chromosomes, they give very distinctly the impression that 

 a difference exists between them in the size of the chromosomes 

 (at any rate as they appear at metaphase of the heterotype 

 division), in the size of the resting nuclei, and correspondingly in 

 the size of entire cells. 



In testing this point the comparison between the two forms 

 was made by means of figures drawn to exactly the same scale 

 with the help of a camera lucida, and by measuring the resting 

 nuclei with an ocular micrometer, the measurements being taken 

 along, and at right angles to, the long axis of such nuclei as were 

 not circular in outline. The drawings and measurements were made 

 upon material which had been carefully fixed, and showed little or 

 no signs of shrinkage during the process. The material was cut 

 in paraffin into sections sufficiently thick to contain entire nuclei 

 Avhich had been untouched by the knife of the microtome. In a 



* "A Preliminary Note on the Chromosomes of Oenothera Lamarckiana and 

 one of its Mutants, 0. gigas." Science, N. S. 26, p. 151, 1907. 



t "The Chromosomes of Oenothera." Ibid. N. S. 27, p. 193, 1908. 



