26 TORREYA 



be made at certain specific times in the plants' growth cycle, or that roots 

 would have to be stored at temperatures low enough to control the utilization 

 of nutrient materials until the cuttings are made. 



Kok-saghyz root segments are very strongly polarized with reference to 

 the initiation of root primordia. As a result it seemed at first to be necessary 

 to plant all the cuttings in their normal vertical positions. More recent work 

 indicates that if the cuttings are placed horizontally, there occurs an apparent 

 displacement of growth substances which induce the formation of many ad- 

 ventitious roots on the lower side of the cutting, and rapid rooting results. 

 Many other problems, including that of disease control are involved in vege- 

 tative propagation. 



Breeding work with kok-saghyz is complicated by the same factor which 

 makes for the tremendous amount of heterogeneity in the populations. The 

 plant is almost, if not completely, self-sterile. One would expect, of course, 

 that a thorough study of populations would reveal the presence of a group 

 of sterility factors operating in such a way as to isolate given genetic blocks 

 of plants. There is some indication that this condition prevails. There is also 

 a suggestion that there is a certain amount of self-fertility during particular 

 periods of the blooming cycle. At any rate the populations are extremely 

 heterozygous. 



Two courses suggest themselves for obtaining more homozygous material. 

 A search may reveal, as it has in many plants, certain individuals with a 

 genetic factor for self-fertility. There is a possibility that such a factor could 

 be combined with otherwise desirable characters. Another approach is to make 

 crosses of such a nature as to put into the progeny a factor for apomixis which 

 is common in other species of Taraxacum. Incidentally attempts at crossing 

 T. kok-saghyz with other species of Taraxacum have brought out the fact 

 that it is diploid while certain other species are tetraploid with respect to the 

 basic chromosome number. 



The chromosome number of T. kok-saghys has been doubled by colchicine 

 treatment and some apparently successful crosses between it and Taraxa- 

 cum megalorrhison, a species with a very high rubber content and some other 

 desirable features, have been made. 



Field cultivation of kok-saghyz presents another whole series of problems. 

 First there is, at least in seed more than a few months old, a seed dormancy 

 which must be overcome to secure uniform germination. Not surprisingly, in 

 view of the heterogeneity of the seed stocks, germination of some seed takes 

 place immediately, while that of others may be delayed for weeks or even 

 months. 



Planting of the seed in the field must be done with great care, particularly 

 with reference to depth of planting in relation to the soil type. The young 

 seedlings are extremely weak and will not emerge if any soil crusting takes 



