Collins : Culture of Crepis 



333 



A CREPIS FLOWER 



Figure 25. Only the outer whorl of florets has opened. At this stage pollen would 

 be, removed from the anthers and the unopened florets would be pulled out, if this 

 flower were to be used for hybridization experiments. Greatly enlarged. 



is utilized, the rest being" pulled out 

 with a pair of fine pointed forceps be- 

 fore anthesis takes place. The efficiency 

 of the improved water depollination 

 method has been well demonstrated in 

 attempts to cross species of which the 

 female, at least, is self fertile, but sets 

 no seed after pollination with foreign 

 pollen. Heads not depollinated set seed 

 abundantly. 



Anthesis occurs during definite inter- 

 vals of the day. In the species under 

 discussion from three to five days are 

 required for all of the flowers of a 

 capitulvmi to open. The outer whorls 

 of florets become active first ; the others 

 follow in order from the outer to the 

 innermost. During clear warm weather 

 anthesis of a whorl of florets com- 



mences before seven o'clock in the 

 morning and ceases about half past 

 eleven the same morning. It is first 

 evidenced in a bud by the rapid elonga- 

 tion of the outer whorl of florets. 

 They remain at the maximum elonga- 

 tion for a short period and then rapidly 

 open. Activity in the process of an- 

 thesis apparently is suspended during 

 the afternoon and until about the same 

 time the following morning when it is 

 renewed. During this period of sus- 

 pended activity the florets tend to re- 

 main in whatever stage they happen to 

 be until the active period of the next 

 day. Thus sometimes only a few of 

 the florets of the first whorl expand 

 during the first active period, the rest 

 remain inactive until the following day. 

 Similar behavior has been noted by 



