30 MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 



during the greater part of the season if the earUest and latest flowers are 

 omitted, (b) A variation in the size of the buds in response to difi"erent con- 

 ditions of the weather. While this variation is not often great enough to be 

 noticeable, there were times at which the buds seemed distinctly larger after 

 several days of warm, humid weather. Both of these difliculties would be 

 rendered comparatively harmless by a collection of a small number of buds 

 each day from each of the lots of plants studied, so that all were being subjected 

 to the same conditions. There are still some elements of error, however, 

 which this method does not fully meet, such, for instance, as the existence of a 

 different period in the different species, or a different kind or degree of reaction 

 to changes in the weather. Without an extensive study of the periodicity and 



response in the several 

 species to changed cli- 

 matic conditions it can 

 not be known just how 

 serious errors these 

 factors introduce, but 

 it is believed that they 

 are slight, (c) There 

 is always present a 

 complete series of 

 buds, beginning with 

 those ready to bloom 

 and ending with those 

 just beginning to de- 

 velop, and the develop- 

 ment is so rapid that 

 buds collected at one 

 hour of the day are 

 not the equivalent of those collected at any other hour. It was found on 

 examination that the buds which would bloom the following day could be 

 readily distinguished by their size and color. Rarely there would be a doubt 

 about some particular bud, and such were omitted from the study. To 

 avoid the collection of buds at different stages of development they were 

 collected from all the lots at 5 p. m. and measured as soon thereafter as pos- 

 sible. This makes all the buds used in these studies as nearly comparable as 

 could well be secured, though it is realized that a source of slight error is to be 

 found in the fact that on some days the development of the buds is more 

 rapid than on others, so that they are not always quite equivalent at the time 

 of collection, when this is determined by the clock without regard to the 

 weather. 



Fig. 9. — Correlation in the buds of OenolheralamarckianafTomlliU'cT- 

 sum. Length of ovary subject, length of hypanthium relative. 

 Coefficient of correlation, 0.3872 ± 0.0453. 



