356 



Colchicine 



Five different chromosomes from Nicotiana langsdorffii, a small 

 flowered species, was studied as trisomic in relation to corolla size. 

 The background into which the extra chromosome was introduced 

 was the hybrid between N. lano;sd()rffii and N. sanderaea, a long- 

 flowered species. ^'^ Since each trisomic could be detected by plant 

 appearance the influence upon particular structures could be ana- 



Control 2n.2n,2n 



8n , 2n. 2n 



2n,8n, 2n 



2n, 2n,8n 



Fig. 14.2 — Diagrams of longitudinal sections through the shoot apex of diploid Datura 

 stramonium t. and three layers of periclinal chimeras. Upper left, diploid layers of 

 tunica and corpus. Upper Right, octoploid tunica and diploid layers beneath. Lower 

 left, first tunica diploid, second tunica octoploid, corpus diploid. Lower right, tunica 

 diploid and corpus octoploid.' (After Blakeslee and Satina) 



lyzed. Three of the five chromosomes, when in trisomies, reduced 

 the corolla in all regions, but two chromosomes decreased one region 

 and increased another. This method was apjjlied to find the relation 

 between whole chromosomal additions and size effects. The con- 

 clusion was reached that size is determined by genes according to a 

 geometric proportion. Eventually, size in Nicotiana flowers can be 

 resolved as a "cumulative geometric effect." ^^ 



Hexaploids combining two species of Gossypium crossed back to 

 G. hirsuium lead to aneuploids with one or two chromosomes from 

 the diploid species introduced in the hexaploid. The characters in- 

 fluenced are: leaf, floral parts, size and shape of bolls, as well as fiber 



