Collins : Culture of Crepis 



335 



fier giving a magnification of three to 

 five diameters. A larger magnification 

 might be desirable, but to secure this 

 would mean a reduction of the working 

 distance and a finer adjustment of 

 focus making it very difficult to per- 

 form the work with the binocular worn 

 on the head of the operator. The in- 

 volucral bracts which inclose the florets 

 in the bud stage are bent down and 

 held out of the way during the opera- 

 tion. The back (or under) side of the 

 corolla thus exposed is slit almost its 

 entire length using a dissecting needle 

 having a very small sharp pointed hook 

 at its tip. The stamen tube is likewise 

 split, often at the same time that the 

 corolla is opened. With the hook at 

 the point of the needle the split stamen 

 tube is pulled from its position sur- 

 rounding the style, the upper end is 

 grasped with finely pointed forceps and 

 removed by a gentle upward pull. The 

 operator can, after a little practice, per- 

 form this without breaking the anther 

 tube, as the fine filaments will break 

 before the stamen tube itself. Some of 

 the pollen grains may adhere to the 

 style, and to remove these the emascu- 

 lated flowers are flushed by a stream of 

 water as in the water depollination pro- 

 cess. Ordinarily only the peripheral 

 whorl of florets are emasculated, the 

 remainder, because of their greater in- 

 accessibility and immaturity, are pulled 

 out. The bracts of the involucre are 

 then folded over the florets and the 

 head enclosed in a small bag. 



When the florets have opened from 

 one to three days later, the heads should 

 be carefully examined for any unemas- 

 culated florets which may have escaped 

 removal. If any open florets are 

 found, the entire head should be 

 discarded; if none are found, pol- 

 len is applied by brushing the anthers 

 of a previously bagged pollen plant 

 over the receptive stigmas of the 

 emasculated florets. It may be desir- 

 able to modify this procedure to take 

 advantage of some particular character- 

 istic of some of the other Crepis 

 species. Thus in C. riihra it is some- 

 times possible to remove both corolla 



and stamen tube at one operation by 

 grasping the upper end of the ligule at 

 an early stage of anthesis and pulling 

 upward steadily and slowly. These 

 parts are detached from the achene 

 and come oft' leaving the style free of 

 pollen and the stigmatic surfaces still 

 unexposed. For the emasculation work 

 the ordinary dissecting needles and for- 

 ceps are very much too coarse and 

 blunt. If satisfactory tools cannot be 

 purchased they can be made by grind- 

 ing down the points, and finishing them 

 under a binocular in order to secure a 

 fine smooth point on the needles and 

 perfect alignment to the tips of the 

 forceps. 



To facilitate the emasculation work, 

 a table has been designed with arm sup- 

 ports similar to the arm supports of a 

 dissecting microscope and an adjustable 

 support for the potted plant which may 

 be raised or lowered so that the buds 

 of the plant can be brought to the level 

 most convenient for the operator. 



Abundant pedigree seed of the self- 

 sterile or partly self-sterile species and 

 biotyi^es may be best secured by dusting 

 the pollen of one plant onto the stigmas 

 of another of the same strain. Some 

 of the strains, due to a high percentage 

 of self -sterility can only be maintained 

 in this way. Self-fertile plants may be 

 protected in the field by using a cheese 

 cloth covered box, but this method is 

 rarely satisfactory for the greenhouse. 

 Semi-transparent waxed paper bags are 

 more desirable than opaque fibre bags. 

 The achenes mature from 3 to 4 weeks 

 after pollination and can be made to 

 germinate without a rest period. 



Parasitic Organisms 



Crepis plants may become infested 

 with parasitic organisms common to 

 greenhouse and cultivated plants and 

 these may be eradicated by the usual 

 methods. During damp, cloudy or rainy 

 weather the greenhouse cultures may be 

 attacked by a fungus (Botrytis cincrea) 

 causing damage to foliage and fre- 

 quently causing death of plants. Reduc- 

 tion of atmospheric humidity seems to 

 be the most effective way to combat the 

 spread of this fungus. 



