CULTURE OF CREPIS FOR GENETIC IN- 

 VESTIGATIONS 



J. L. Collins 

 University of California, Berkeley, California 



IN genetic investigations dealing with 

 living organisms the problems of 

 cultural technique are of prime im- 

 portance. The methods must permit of 

 facility and accuracy in manipulation 

 and at the same time give equal and 

 optimum conditions for the develop- 

 ment of all individuals. In most breed- 

 ing w^ork, such technique is only de- 

 veloped after a period of trial and 

 comparison by w^hich unsuitalile methods 

 are discarded. 



Preliminary experiments indicate that 

 some species of the genus Crepis, par- 

 ticularly those w^ith low^ chromosome 

 numbers, give promise of becoming the 

 means of inquiring into problems of 

 cytology, the evolution of chromosome 

 number, speciation, and heredity in 

 plants. Since a number of inquiries 

 concerning technique have been re- 

 ceived it seems desirable to describe 

 some of the cultural and hybridization 

 methods which have been employed by 

 the Division of Genetics at the Univer- 

 sity of California in preliminary ex- 

 periments with Crepis plants. 



The genus belongs to the chicory 

 tribe or Liguliflorse of the Compositse 

 which includes all those plants having a 

 flower capitulum composed entirely of 

 ligulate flowers. In Crepis capillaris 

 each flower is perfect, 30 to 50 l)eing 

 grouped to form a single capitulum 

 which when open measures about 20 

 mm. in diameter. 



Although the cultural and hybridiza- 

 tion methods reported here have been 

 used on relatively few species, they may 

 be adapted for use on any of the small- 

 seeded plants of this group. 



Germination of Achenes 



The achenes are very small and the 

 seedlings on first appearance may 

 closely resemble those of some weeds, 



therefore, the method of germination 

 must be so devised as to permit no un- 

 certainty regarding the identity of the 

 seedlings. This has been provided for 

 in two ways, one of which is steam 

 sterilization of the soil in shallow clay 

 seed pans at 15 pounds pressure for 45 

 to 50 minutes. Before sterilization a 

 piece of paper is tied over the top of 

 the seed pans and it is not removed 

 until the achenes are planted, thus 

 eliminating chances of contamination if 

 seeding is delayed for some time after 

 sterilization. The achenes are sown in 

 the pans and covered as in the usual 

 practice for seeds of this size. About 

 the time the second plumule leaf ap- 

 pears the seedlings are pricked out and 

 planted in six-inch clay flower pots, or 

 into smaller pots or flats, if the plants 

 are to be grown as field cultures. In 

 the second method the seeds are placed 

 in a small moist-chamber germinator 

 shown in figure 23, suitable for any 

 number up to 1 00 achenes. 



Glassware and paper should be ster- 

 ilized to prevent the growth of fungi in 

 the moist chamber. This latter method 

 has an advantage over the sterilized 

 soil by permitting inspection of the 

 sprouting achenes, an accurate record 

 of the percentage of germination, the 

 examination of. achenes that fail to 

 germinate, and a record of the sequence 

 of germination. As the achenes germi- 

 nate they can be taken up with a fine 

 pair of forceps and planted in pots or 

 flats. In order to avoid injuring the 

 tender seedlings by handling with the 

 forceps, a small portion of the damp 

 towel paper may be lifted with the 

 seedling adhering to it. This fragment 

 of paper is placed in the soil with the 

 plant, the forceps not coming in con- 

 tact with the seedling at any part of the 

 process. Some achenes which remain 



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