1929] Navashin: Triploidi/ in Crepis 379 



Crepis capillaris is especially favorable material for study, for it 

 is distinguished from other plants which have been investigated 

 hitherto by its low chromosome number (n = 3) as well as by very 

 clear morphological features of the individual chromosomes, the latter 

 circumstance permitting unmistakable identification even under most 

 unfavorable conditions. This species has therefore been chosen as the 

 principal subject of the investigations ; and triploidy has been investi- 

 gated less full>' in two other species, chiefly for the sake of com- 

 parison with the conditions found in C. capillaris. As will be seen 

 later such a comparison has proved interesting. 



A single triploid plant, "1947," of C. capillaris was the source 

 of the material of the present investigation ; similarly a single plant 

 of each of the other two species (C fectoriim and C. dioscoricHs) } 



The somatic chromosomes of triploid plants of C. capillaris are 

 shown in plate 56. As may be seen from the drawings, the homo- 

 logous chromosomes in a triploid individual are present in threes 

 instead of twos ; their size and shape as well as the most minute details 

 of their organization (the satellites and their size) are wholly un- 

 affected under triploid conditions. The metamorphoses of the chromo- 

 somes during the prophase of mitosis differ in no way from those 

 known to occur in a normal diploid nucleus. 



Special attention should be drawn here to the remarkable relation 

 between the satellite and the nucleolus in the prophase of the somatic 

 division. As was first pointed out sixteen years ago by S. Navashin 

 (1912, 1927), the satellite originally appears in the prophase on the 

 surface of the nucleolus, and becomes attached at a certain stage 

 of karyokinesis by a very thin thread to a particular end of a specific 

 chromosome. The writer's observations on triploids have revealed 

 the same phenomenon with the sole difference that three satellites are 

 formed instead of two as in diploids. Two stages of this process 

 of satellite formation are shown in plate 56, a and h. It should be 

 added, however, that such observations are rather difficult, success 

 depending entirely upon perfection of technique. The fixing fluid 

 introduced by S. Navashin (chromic acid, formalin, and acetic acid 

 in varied proportions), which has become popular among cytologists 

 under various names, gives the be.st results inasmuch as the nucleolus 

 becomes completely destained ; on the other hand, with Flemming's 

 solution and most of the other usual fixatives the nucleolus is as 

 deeply stained by haematoxylin as the chromosomes themselves. It 



1 The first triploid plant of C. dioscnridis was found by Mrs. G. B. Medvedeva. 



