502 CocKERELL: NorTH AMERICAN SPECIES OF HYMENOXYS 
rays) only about 9 mm. diameter! At this point I find myself in 
a difficult position. I am unable to define 1. chrysanthemordes, 
subsp. multiflora, and the allied forms in such a way as to abso- 
lutely separate them. As in the Richardsoni-series, the extremes 
are so different that it seems ridiculous to think of them as allied, 
but there are innumerable intermediate forms, and structural dif- 
ferences of any consequence simply do not exist. As in Matr- 
caria etc., these plants no doubt differ greatly according to the 
amount of moisture they get, specimens from very dry places 
being extremely small. At the same time, it is evident that genuine 
racial differences exist, and these, so far as they can be discerned, 
may very well be made the basis of subspecific names. To de- 
termine the minute characters I examined microscopically the 
achenes, pappus and corollas of plants from Oklahoma, Kansas, 
Texas, Chihuahua, New Mexico, and Arizona. The pappus-scales 
were practically alike in all, with quite long points ; in color they 
were ferruginous of various shades, uniformly light in material 
from Texas and near Tucson, Arizona, more especially ferruginous 
at base in some from Las Cruces, N. M., and near Chihuahua. 
The achenes were essentially the same, as also the disc-corollas. 
The bracts vary as they always do in the genus, but the differ- 
ences are unimportant. The high broad receptacle is sometimes 
(¢. g., Chihuahua material) narrower and more conical, but the 
differences are not striking. 
Mr. M. L. Fernald (Am. Jour. Sci. 14: 189), facing a very 
similar condition in Betula, writes: “ But since it is obviously im- 
practicable to regard all these forms as one species, it seems wiser 
to recognize the more marked centers of variation as species 
which are admitted to pass by exceptional tendencies to other 
forms ordinarily distinguished by marked characteristics.” Of 
course it is true that species which are quite distinct in actual fact 
may seem to intergrade, because of the variation in the characters 
taken as specific. For example, Helix nemoralis is a snail having 
the lip of the shell black or nearly so, while the closely similar 
Helix hortensis has the lip white. There occur varieties of 7 
nemoraiis in which the lip is pallid or even white, and varieties of 
Hf. hortensis in which it is black. These facts led some g 
authorities to treat hortensis as a variety of nemoralis, until it was 
