216 TAXONOMIC STUDIES IN THE GENUS CERASTIUM : I 



The Character Pollen Size 



This character does not appear to have been used previously for differentiating 

 between the Cerastium taxa. It appears, however, to be of considerable diagnostic 

 value, especially in distinguishing between C. atrovirens and C. suhtetrandrum. As with 

 the character seed size, it would appear that cultural conditions do not materially affect 

 its constancy. This was shown by the experiment already described above. 



Examination of the three groups showed that, as with seed size, there is a considerable 

 overlap of the variation in each primary group, together with a central range of variation 

 common to all groups. Although the means are significantly different it is not possible 

 to use this character by itself for distinguishing between the groups. The actual figures 

 obtained were as follows : 



Standard error of Actual difference 



Groups dfference between means between means 



A and B 7-84 21-01 



B and C 0-30 28-37 



AandC 0-86 7-36 



The Character Sepal/Petal Ratio 



This character is referred to in many floras. Lid (1944) states that in C. atrovirens 

 and C. semidecandrum the calyx is larger than the petals. Lindman (1918) states that 

 C. pumilum and C. glutinosum have petals as long as the calyx, whilst by implication 

 C. atrovirens, C. semidecandrum and C. subtetrandrum have petals shorter than the calyx. 

 It is further stated that C. subtetrandrum has long, acutely-pointed sepals. Schinz & 

 Keller (1909) state that the petals are as long as the calyx in C. pumilum and shorter 

 in C. semidecandrum. Coste (1901) makes similar statements about these species. No 

 details are given, however, of the precise value of the ratio sepal length/petal length. It 

 was considered that this character might be of importance in distinguishing between 

 the three groups. 



The data for the means for this character are shown below : 



Standard error of Actual differences 



Groups difference between means between means 



A and B 1-17 16-87 



BandC 2-58 17-81 



AandC 2-54 1-04 



It can be seen that, although the means for this character show significant differences 

 between groups B and C and B and A, the difference between the means of A and C 

 is not significant. The variation of this character was examined in the experimental 

 plants and although no significant differences resulted from the different treatments, there 

 was greater variation throughout than with the two previous characters. 



The Character of Bract Length/Scarious Tip 



This character is one of the most frequently mentioned as being of importance 

 diagnostically and the importance attached to it is fully justified by its high discriminant 

 value in the analysis described later. In the experimental treatment of plants, since it 

 was C. atrovirens that was grown and, indeed, a population characterised by the her- 

 baceousness of its bracts, little or no difference could be found between the bracts of the 

 different plants. 



