166 



GENUS CHRYSOTHAMNUS. 



lengths as well as the extent of variation for each of the major species is given in table 

 17, while tables 22 and 23 (p. 207 and p. 230) give similar data for the more common 

 forms of two of the larger species. 



The depth to which the corolla-limb is cleft, that is, the length of the corolla-lobe, 

 has been used as a diagnostic character for many proposed species. The actual length, 

 however, has never been given (except in a recent paper by one of the present authors) 

 and the relative length, if mentioned at all, is stated in terms so general as to indicate 

 that measurements have not been made. When a large series of specimens are meas- 

 ured, it is found that the absolute length of the lobe as well as the ratio between lobe- 

 length and corolla-length usually exhibits considerable variation within a single species. 

 The exceptions are C. paniculaius and C. teretifolius, both non-plastic species in which 

 the lobes are constantly near 1 mm. in length, and C. albidus, in which they have the 

 remarkable length of 2 to 2.5 mm. Even within the "small species" of some botanists, 

 that is, the subspecies of the present treatment, the range of variation in the length of 

 the lobe is too great to permit of rigid application. It is very useful, however, as indi- 

 cating certain tendencies and can sometimes be correlated with other characters and 

 with geographic distribution. This is especially noticeable in the case of three close 



Table 17. — Length of corolla and of corolla-lobes in the species of Chrysothamnus. 



No. of 

 collections 

 measured. 



Length of 



including 

 lobes. 



Length of 

 coroUa- 

 lobes. 



Ratio of 



lobe-length 



to total 



length. 



Punctati : 



C. paniculatus. 



C. teretifolius. . 

 Typici: 



C. gramineus . . 



C. vaseyi 



C. viscidiflorus. 



C. greenei 



C. albidus 



Pulchelli: 



C. pulchellus. . , 



C. depressus. . . , 

 Nauseosi: 



C. pyramidatus 



C. parryi 



C. nauseosus. . . 



e.Oto 6.2 



6.0 6.5 



12.0 



6.6 6.5 



4.5 7.0 



4.0 4.5 



7.0 8.0 



0.8 to 1.2 

 1.0 1.2 



per cent. 

 13 to 18 



per ceni. 

 15.4 

 16.7 



21 

 7 25 

 6.5 32 



' Computed by taking the average of all of the individual ratios. 



subspecies of C. nauseosus included in table 23 (p. 232). These are pinifoHus, of Colorado 

 and adjacent States, with lobes which average only 0.9 mm. long (0.7 to 1.3 mm.); 

 consimilis, which has its center of distribution in Nevada and in which the lobes average 

 1.3 mm. long (1 to 1.6 mm.); and viridulus, of eastern California, in which the lobes 

 average 2.0 mm. long (1.7 to 2.5 mm.). These three subspecies, all inhabitants of 

 alkaline soils, differ only in the lobe-lengths and in a few minor tendencies, robustness, 

 inflorescence, etc., which can be correlated only partially with this. The overlapping 

 in the lobe-length occurs most frequently in specimens from localities where the ranges 

 meet, so that some individuals can not be definitely placed. This variation with geo- 

 graphic distribution is paralleled in certain other characters and is representative of a 

 tendency of frequent occurrence, namely, that within a given series of forms the greatest 

 floral development is among those of westerly or southwesterly distribution. Thus, in 

 C. nauseosus the maximum and also the highest average length of both involucre and 

 corolla are reached in the subspecies mohavensis and bernardinus of the Southwest (see 

 table 23). Similarly within the subspecies spedosus it is found that specimens from 



