The Origin of Crepis and Related Genera 23 



gree of specialization of the involucre and secondarily by the 

 amount of specialization of the achenes. In Catonia, as the fruits 

 mature, the involucre merely increases in size and the bracts may 

 become somewhat thicker and indurate but with litde, if any, 

 change in shape. In the other two subgenera, the bracts of fruit- 

 ing heads have a median dorsal keel and become more or less 

 swollen at the base by development of soft spongy tissue. The 

 achenes in Catonia and Eucrepis are not as a rule provided with 

 a true beak, the slender stipe bearing the pappus, but in Barl^^- 

 hausia the beak is always present. There are naturally certain 

 exceptions to these generally reliable distinguishing features, but 

 such exceptional species usually exhibit some marks of re- 

 semblance to other species whose subgeneric affinity is clearly 

 marked. In general it is obvious that there is increasing special- 

 ization of the involucre and the fruits as one passes from Catonia 

 through Eucrepis to Bar\hausia. Along with this increasing 

 specialization there is a definite trend toward reduction in length 

 of life. All the species of Catonia are perennials, while about 

 one-fourth of the Eucrepis species and three-fourths of the Bar\' 

 hausia species are annuals. 



A somewhat similar situation exists in the three subgenera 

 with reference to the proportion and nature of endemic species. 

 Although some species are so rare or poorly represented in 

 herbaria that the extent of their distribution is wholly conjec- 

 tural, yet the distribution of the majority is sufficiently known 

 to classify them as either restricted to a single geographical unit 

 or of wider extent. In this sense, the proportion of endemics in 

 Catonia is about one-half; in Eucrepis one-third, and in Bar\' 

 hausia less than one-third of the species are thus restricted. 

 Furthermore, on the basis of relative degree of specialization 

 through reduction in size of plant and its parts, increase in num- 



