1 88 BOTANICAL GAZETTE [march 



Constancy in the number of chromosomes. — After the appearance 

 of Strasburger's classical paper (23) on "Periodic reduction of the 

 number of chromosomes in the life-history of living organisms," 

 investigators of many forms added to the evidence in favor of the 

 proposed theory. A plant is known to have a certain number of 

 chromosomes, without much variability, in one phase of its life-history 

 When the number is not too great, an accurate counting is not difficult. 

 The larger the number, however, the more difficult the counting 

 becomes, especially when the chromosomes are long and filamentous, 

 because the stages favorable for exact counting then become more 

 and more narrowly limited. 



Unfortunately the rarity of the favorable stages has led some 

 investigators to the hasty conclusion that the counting is almost 

 impossible, while others, being unable to find the favorable stage, 

 have tried to make a rough estimate of the number from such stage - 

 as they had. It is no wonder that such rough estimates, based upon 

 stages unfavorable for counting, should vary. It is curious to note 

 that even in Nephrodium molle, which contains 66 chromosomes in 

 the gametophyte and 132 in the sporophyte, the number was clearly 



1 



rmal 



counted by the author both in apogamous and in normal forms 

 while Farmer and Digby (5) claimed that the number of chromo- 

 somes varied in the allied forms of Nephrodium molle which they 

 studied. The constancy in the number of chromosomes in no 

 cases has been cited as one of the important proofs of the individuality 

 of the chromosome, and the importance of this theory in any discus- 

 sion of heredity cannot be neglected. 



In the present investigation of Fucus vesiculosus, the number ot 

 chromosomes was counted in mitoses in the vegetative cells of male 

 and female plants, in the antheridium, in the oogonium, and in 

 sporelings. In the vegetative cells, from the polar view of both early 

 metaphase (figs. 3, 0) and anaphase (figs. 6; 12a, b), 64 chromosomes 

 were counted. Although the antheridium is very small, the polar 

 view of the mitotic figures in early metaphase showed clearly the same 

 number, as 32 bivalent chromosomes in the first division and 3 2 

 univalent chromosomes in the mitoses following the second division- 

 In the first mitosis in the oogonium 32 bivalent chromosomes ar 

 present (figs. 47 , 4 8, 52 ) an d, as in the antheridium, 32 univalent om 



