220 University of California Publications in Agricultural Sciences [Vol. 7 



flower head was considered fully open when all the disc florets had 

 opened and the stigmas were projecting. This stage is usually main- 

 tained for two or three days. Then the capitula widen and spread out, 

 and measurements taken at this stage always give results which are 

 about 3 mm. more than the actual diameter when the heads are fully 

 open. Moreover the flowers open at about 9 a.m. on bright days and 

 remain open till after 3 p.m. if the day is not hot. But on dull and 

 cloudy days they open about 10 a.m. or later, and occasionally they 

 fail to open altogether. The 25 flowers first formed were measured 

 in every case and their individual measurements noted. Inflorescence 

 in Crepis closely follows the type described by Gleason (1919) for 

 Vernonia mussurica. The main axis is the first to give off flowers, 

 and the few branches at the top are more or less leafless. The flowers 

 form a more or less flattened corymb at the top. The lower nodes 

 bear shorter and frequently less developed lateral branches which 

 usually appear so late in the season that none of the heads, or only 

 a part of them, open their flowers and set seed before the plant has 

 exhausted itself and dies down. In Vernonia three types of varia- 

 tions were investigated: (1) a variation between the heads of each 

 cyme, possibly correlated with their position whether terminal or 

 inferior; (2) a variation between different floriferous branches of the 

 same plant possibly correlated with the amount of available nourish- 

 ment; (3) a general variation between different individuals, possibly 

 correlated with the size and vigor of the plant and therefore indirectly 

 with the habitat. Gleason finds that within a single cyme of from 

 two to six heads the terminal head is the largest. In larger cymes, 

 some of the secondary terminal heads are frequently larger than the 

 primary terminal head, the number of flowers is greatest for the 

 terminal head of each cyme, but it is relatively constant for each 

 individual plant. Two sets of factors, which may be environmental, 

 or hereditary, or both, are involved. One determines the number of 

 heads produced and the other the average number of flowers in each 

 head. These act upon the plant independently and thus give four 

 classes : many large heads, many small heads, few large heads, and 

 few small heads. This investigator based his measurements and con- 

 elusion on 25 flowers. Goodspeed and Clausen (1915) estimate 25 as 

 the minimum number on which to base any calculations for flower 

 size. Goodspeed and Clausen (1918) have described a mechanical 

 apparatus by which measurement of flowers is made. East uses only 

 a millimeter scale ; I have followed East in this work. 



