Collins : _ Culture of Crepis 



331 



pots. However, the later are more 

 satisfactory. 



Different forms of fungus may ap- 

 pear and grow very rapidly in the moist 

 chamber of the germinator, the spores 

 having been introduced with the 

 achenes. Achenes are sometimes re- 

 tarded or entirely prevented from ger- 

 minating by the presence of fungi in 

 the germinator. Although it is not 

 always necessary, in special cases of 

 limited supply of seed it may be desir- 

 able to treat the achenes to prevent 

 fungus development in the germinator. 

 Formalin vapor and calcium hypo- 

 chlorite have been used effectively for 

 this purpose, but any of the common 

 methods of seed sterilization may be 

 used. 



Technique of HyDridization 



The smallness and peculiar arrange- 

 ment of the flower parts in Crepis re- 

 quire, for critical hybridization work, 

 especially devised methods of manipu- 

 lation. Mendel attempted some hybri- 

 dization work on Hieracium, the 

 flowers of which are essentially like 

 those of Crepis. He found that the 

 failure to secure a large number of 

 hybrids was largely due to the minute- 

 ness of the flowers, to their peculiar 

 arrangement, and to the fact that it 

 was seldom possible to remo^'e the 

 anthers without injuring the pistil. 



Although the flowers of Crepis capil- 

 laris and C. tcctormn are no larger than 

 those of Hieracium the difficulties men- 

 tioned by Mendel have now been largely 

 overcome by growing plants in the 

 greenhouse where humidity can be con- 

 trolled, and by using especially adapted 

 tools for the work. The most useful 

 of these is a binocular magnifier, which 

 can be attached in place before the eyes 

 of the operator, thus leaving both hands 

 free. IMicroscopes of this type can be 

 obtained from optical companies. 



In C. capillaris, the anthers are re- 

 moved just before the flowers of the 

 capitulum open, when the bud is about 

 7 mm. long. When the flower is fully 

 open about half of this length is bent 

 back so as to be in a plane at right 

 angles to the pedicle. Individual flowers 



when fully expanded are from lo to 

 12 mm. long. The length of the pistil 

 is slightly less than that of the corolla. 

 The stamen tube of a fully open flower 

 is 3 mm. in length. The flower at the 

 stage when emasculation is performed 

 is but 5 mm. long. Flowers of the 

 Compositse have five anthers, which 

 form a tube about the style, the pollen 

 being shed on the inside of the tube. 

 As the flower begins to open, the style 

 elongates, pushing the two closely ap- 

 pressed stigma lobes upward through 

 the stamen tube until they extend above 

 it, when they spread apart and are later 

 pollinated. The upper portion of the 

 surface of the style and the outer sur- 

 face of the stigmas are supplied with 

 barbs pointing upward, which sweep 

 the pollen out of the tube as the style 

 elongates. The stigmatic lobes of the 

 style usually remain together until the 

 floret is fully open, and the style fully 

 extended, thus preventing self-fertiliza- 

 tion from taking place before there is a 

 chance for cross-fertilization. If they 

 fail to be cross fertilized, the stigmas 

 curl in such a way that the receptive 

 inner surface of the stigma comes into 

 contact with its own pollen or that of 

 an adjacent floret so that fertilization 

 may result. 



Two methods of pollen removal re- 

 ferred to in a previous paper (2) have 

 been used. The first method consists in 

 removing the pollen from the stigmas of 

 the entire head, by forcing a fine jet of 

 water over them from the nozzle of a 

 small dental chipblower syringe, much 

 after the method described by Oliver. 

 Due to the fact that anthesis occurs 

 progressively from outer to inner florets 

 of the capitulum, this method was not 

 satisfactory, because it would require 

 close attention for a number of hours 

 on several successive days to insure the 

 removal of the pollen from all the 

 florets. 



A modification of the Oliver method 

 has been devised which reduces the 

 time and attention required for a given 

 pollination, and with which the prob- 

 ability of self-pollination is reduced to 

 a minimum. In this method only the 

 outer whorl, containing about 20 florets 



