Section 13 — Plant Genetics and Breeding 



varieties and to a lesser extent among species. 



In order to evaluate the importance of embryo 

 size variations within varieties, it was necessary 

 to eliminate the influence of endosperm using 

 two different approaches. The first was to isolate 

 large and small embryos, place them on a suitable 

 culture medium and look for differences among 

 the derived plants. The second was to compare 

 plants derived from seeds of the same weight 

 which however had embryos of different sizes. 

 This last approach became possible after a care- 

 ful study of the means by which embryo varies 

 in relation to the endosperm at different places 

 in the spike. 



It was found that kernels of the same weight 

 have not necessarily the same size of embryo. 

 This depends mainly on the position of the kernel 

 in the spike and on the variety. 



The differences among large and small em- 

 bryos consist primarily of differences in the 

 number or degree of development of basic pri- 

 mordia, namely, those of the seminal roots, 

 of the three first leaves and of the tiller at the 

 base of the coleoptile. 



Large embryos in comparison to small embryos 

 gave plants with greater (a) number and length 

 of seminal roots, (b) number and length of the 

 first leaves, (c) number of tillers, (d) weight of 

 green matter, and (e) number of spikelets per 

 spike. 



Varieties show differences in the size of embryo. 

 Varieties with comparatively large embryos 

 were found to have a greater competative ability 

 in mixtures, a greater number of seminal roots, 

 and a greater tillering capacity. 



The tendency was for varieties with relatively 

 large embryos to fit better on soils of lower fer- 

 tility and lower water-holding capacity. 

 The opposite was true for varieties with small 

 embryos. This tendency is also supported by the 

 observation that Triticum durum wheats which 

 were found to have on the average embryos 

 of greater size than Triticum vulgare wheats 

 show better adaptability in drier regions. 



In this work are discussed in detail the bear- 

 ings of the results on the breeding of wheat, as 

 well as the importance of endosperm in relation 

 to the biological significance of double fertiliza- 

 tion. 



13.108. (D.) Pictorial Technique in the Genetical 

 Analysis of Horticultural Crops in Scotland. 



A. B. Wills (Dundee, Great Britain). 



rescence. The ideogram method of Anderson and 

 Schregardus allows a graphical comparison of 

 variation in internode patterns and so provides 

 a partial analysis of habit. The method is adapt- 

 able and can be used for the comparison of 

 genotypes within species or genera. Diagrams and 

 preserved plant material will demonstrate the 

 method used at Mylnefield in the analysis of 

 tomatoes and Ribes species, with particular 

 emphasis on adaptation in these crops. 



Evidence will be presented that tomatoes of 

 determinate growth, with either shorter inter- 

 nodes or fewer internodes, probably have evol- 

 ved from determinate types. Further evolution 

 has given rise to dwarf varieties with fewer, 

 shorter internodes and dwarf bushy types in 

 which apical dominance is suppressed. 



The selection of suitable material and construc- 

 tion of the ideograms of woody perennials pres- 

 ent special problems. The methods devised to solve 

 these problems in the genus Ribes will be illustra- 

 ted. It is believed that differences between ideo- 

 grams of black currant varieties reflect adapta- 

 tion to different environments, whereas the 

 heavy pruning practised on red currants leads 

 to similar ideograms in many varieties. 



; is a iunaamental characteristic of 

 plants which is partially dependent on the inter- 



ittprn nf thp vpuptativp shnnt anH infln- 



Habit is a fundament 



piaius wnicn is paruany aepenaeni on ine inter- 

 node pattern of the vegetative shoot and inflo- 



13.109. Inheritance of Awnedness and Glume Colour 

 in Some New Vulgare Wheat Varieties. A. A. 

 Omar, A. K. A. Selim and S. H. Hassanein 

 (Cairo, Egypt). 



1. The inheritance of awnedness was studied 

 on the F2 and F3 generations of eighteen crosses 

 including nine varieties. This character was found 

 to be affected by three pairs of genes. The gene 

 Bi for apically awnleted, B2 for short awned, 

 the combinations Bi, B2 for awnless and the 

 recessive genes bi, b2 for fully awned type. The 

 gene A was suggested as a promoter for tips 

 and awns and its recessive allele (a) has no 

 effect. The interaction of these genes gives rise 

 to new types as B1-B2-A- for awnless beak, 

 Bi-b2b2A- for long apically awnleted ap- 

 proaching awnleted and bibiB2-A- for short 

 awned approaching fully awned. 



2. The parental varieties were arranged in 

 three classes: awnless, apically awnleted and fully 

 awned. The awnless class includes the variety 

 Ramona with the genes B1B2A. The awnleted 

 class includes the varieties N.A.101 and hatcher 

 with genes Bib2a. The fully awned classes in- 

 volve the varieties Giza 144, Giza 145, Giza 147, 

 Giza 139, Lee and Mida with the genes bib2a. 



3. The inheritance of glume colour was studied 

 on the F 2 and F 3 or eight crosses including six 



247 



