368 University of CaUfornia Publications in Agricultural Sciences [Vol. 2 



the particular aim of tracino: the satellites through the meiotic stages. 

 If this could be done it would add materially to the genetic signifi- 

 cance of satellites, as it would show that they are not only a peculiar 

 structure of the somatic metaphase chromosomes, but are also a part 

 of the chromosome which is permanently differentiated out from the 

 rest of the chromosome. 



In many species of plants it has been found that certain pairs 

 of the somatic metaphase chromosomes have definite and constant 

 constrictions. In TrifoUum the constrictions are not easily observed 

 on account of the small size of the chromosomes. Some constricted 

 pairs were established in several species, but an intensive study would 

 probably reveal more constricted chromosomes. The constrictions are 

 all subterminal. 



In general there is not a great variation in chromosome size within 

 the haploid sets in TrifoUum. Some species, however, show con- 

 spicuous size differences, such as T. alexandrinum (fig. 2d), T. incar- 

 natwm (fig. 2c), T. hyhridum (fig. 2e), and T. reflexum (fig. 1/). 

 The chromosome morphology of the species was studied with two main 

 objectives in view : 



1. In order to be able to distinguish each member or at least the 

 groups of a haploid set. This is usually done in combination with a 

 genetic analysis, by which method it is possible to assign a particular 

 gene to a particular chromosome. 



2. In order to compare the chromosome complexes in species of 

 the same genus and by this method to study their relationship and 

 origin. It has now come to be used also in practical plant taxonomy 

 to determine, in cases of doubt, whether nearly related forms should 

 be ranked as distinct species. The first problem has been the chief 

 concern of the present study of chromosome morphology in species 

 which seemed the most promising from a genetic standpoint. In these 

 species the following features of chromosome individuality have been 

 revealed : 



T. pratense: 



1 pail- of satellited c-lnomosomes, G pairs of about equal size, without 

 visible constrictions. 



T. incarnatum : 



1 pair of satellited chromosomes. 



1 pair of large, constricted chromosomes. 



2 pairs of medium, constricted chromosomes. 



3 pairs of medium chromosomes without visible constrictions. 

 1 pair of small, constricted chromosomes. 



